Are you planning for a big SharePoint implementation: Intranet, Exrtanet, Web Portal, Document Management ...etc? Well you definitely chose the right technology. Just keep in mind these limitations and guidelines for the best SharePoint 2007 implementation. Good luck!

These are the official known limitations for MOSS 2007 with the best performance advises. Have a CLOSE look:

Site Object

Site object	Guidelines for acceptable performance	Notes	Scope of impact when performance degrades
Site collection	50,000 per content database	Total farm throughput degrades as the number of site collections increases.	Farm
Site collection	150,000 per Web application	This limit is theoretical, and is dependent largely upon: Performance of the database server on which the configuration database resides. Performance of the Web servers in the farm. Network bandwidth between the Web servers and the database server. This is not a hard limit, and assumes a single database server. Your environment may not be able to host this many site collections per Web application. Distributing content databases across additional database servers can increase the effective limit of the number of site collections per Web application. You should perform testing to determine the actual effective limit in your environment.	Farm
Web site	250,000 per site collection	You can create a very large total number of Web sites by nesting the subsites. For example, 100 sites, each with 1000 subsites, is 100,000 Web sites. The maximum recommended number of sites and subsites is 125 sites with 2,000 subsites each, for a total of 250,000 sites.	Site collection
Subsite	2,000 per Web site	The interface for enumerating subsites of a given Web site does not perform well as the number of subsites surpasses 2,000.	Site view
Document	5 million per library	You can create very large document libraries by nesting folders, using standard views and site hierarchy. This value may vary depending on how documents and folders are organized, and by the type and size of documents stored.	Library
Item	2,000 per view	Testing indicates a reduction in performance beyond two thousand items. Using indexing on a flat folder view can improve performance.	List view
Document file size	50MB (2GB max*)	File save performance is proportional to the size of the file. The default maximum is 50 MB. This maximum is enforced by the system, but you can change it to any value up to 2 GB.	Library, file save performance
List	2,000 per Web site	Testing indicates a reduction in list view performance beyond two thousand entries. For more information about large lists, see White paper: Working with large lists in Office SharePoint Server 2007.	List view
Field type	256 per list	This is not a hard limit, but you might experience list view performance degradation as the number of field types in a list increases.	List view
Column	2,000 per document library 4,096 per list	This is not a hard limit, but you might experience library and list view performance degradation as the number of columns in a document library or list increases.	Library and list view
Web Part	50 per page	This figure is an estimate based on simple Web Parts. The complexity of the Web Parts dictates how many Web Parts can be used on a page before performance is affected.	Page
Managed path	20 per Web application	20 managed paths is a soft limit. Managed paths are cached on the Web server, and CPU resources are used to process incoming requests against the managed path list. You should test for performance before exceeding 20 managed paths in a single Web application.	Web application

People Object

People object	Guidelines for acceptable performance	Notes
Users in groups	2 million per Web site	You can add millions of people to your Web site by using Microsoft Windows security groups to manage security instead of using individual users.
User profile	5 million per farm	This number represents the number of profiles which can be imported from a directory service, such as Active Directory, into the people profile store.
Security principal	Approximately 2,000 per ACL (Access Control List) on any securable object (scope)	The total size of the ACL on scopes can be no larger than 64kb. Because each security principal is approximately 32 bytes in size, there can be no more than approximately 2,000 security principals or less for each scope. If this limit is reached, indexing of items in that scope, and all items below that scope, to fail. Also, because SharePoint Groups are expanded during the indexing process, having more than 2,000 users or Directory Groups in a SharePoint group and using that group for securing scopes may cause indexing of items secured with these groups, and all items below them, to fail. This limit only occurs when Windows Integrated Authentication is utilized.

People object

Guidelines for acceptable performance

Notes

Users in groups

2 million per Web site

You can add millions of people to your Web site by using Microsoft Windows security groups to manage security instead of using individual users.

User profile

5 million per farm

This number represents the number of profiles which can be imported from a directory service, such as Active Directory, into the people profile store.

Security principal

Approximately 2,000 per ACL (Access Control List) on any securable object (scope)

The total size of the ACL on scopes can be no larger than 64kb. Because each security principal is approximately 32 bytes in size, there can be no more than approximately 2,000 security principals or less for each scope. If this limit is reached, indexing of items in that scope, and all items below that scope, to fail.

Also, because SharePoint Groups are expanded during the indexing process, having more than 2,000 users or Directory Groups in a SharePoint group and using that group for securing scopes may cause indexing of items secured with these groups, and all items below them, to fail.

This limit only occurs when Windows Integrated Authentication is utilized.

Search Object

Search object	Guidelines for acceptable performance	Notes
Search indexes	One per SSP Maximum of 20 per farm	Office SharePoint Server 2007 supports one content index per SSP. Given that we recommend a maximum of 20 SSPs per farm, a maximum of 20 content indexes is supported. Note that an SSP can be associated with only one index server and one content index. However, an index server can be associated with multiple SSPs and have a content index for each SSP.
Indexed documents	50,000,000 per content index	Office SharePoint Server 2007 supports 50 million documents per index server. This could be divided up into multiple content indexes based on the number of SSPs associated with an index server.
Content sources	500 per SSP*	This is a hard limit enforced by the system.
Start Addresses	500 per content source*	This is a hard limit enforced by the system.
Alerts	1,000,000 per SSP	This is the tested limit.
Scopes	200 per site	This is a recommended limit per site. We recommend a maximum of 100 scope rules per scope.
Display groups	25 per site	These are used for a grouped display of scopes through the user interface.
Crawl rules	10,000 per SSP	We recommend a maximum 10,000 crawl rules irrespective of type.
Keywords	15,000 per site	We recommend a maximum of 10 Best Bets and five synonyms per keyword.
Crawled properties	500,000 per SSP	These are properties that are discovered during a crawl.
Managed properties	100,000 per SSP	These are properties used by the search system in queries. Crawled properties are mapped to managed properties. We recommend a maximum of 100 mappings per managed property.
Authoritative pages	200 per relevance level	This is the maximum number of sites in each of the four relevance levels.
Results removal	100	This is the maximum recommended number of URLs that should be removed from the system in one operation.
Crawl logs	50,000,000	Number of individual log entries in the crawl log.

Logical Architcure

Logical architecture object	Guidelines for acceptable performance	Notes
Shared Services Provider (SSP)	3 per farm (20 per farm maximum)
Zone	5* per farm	The number of zones defined for a farm is hard coded to 5.
Web application	99 per SSP	This limit includes the number of Web applications on child farms consuming resources on this SSP.
Internet Information Services (IIS) application pool	8 per Web server	Maximum number is determined by hardware capabilities.
Site collection	50,000 per Web application
Content database	100 per Web application
Site collection	50,000 per database

Physical Objects

Physical object	Guidelines for acceptable performance	Notes
Index servers	1 per SSP*
Application servers running Excel Calculation Services	No limit
Query servers	No limit	Because 100 content databases are supported for each query server, the number of query servers required per farm is based on the number of content databases in the farm. For example, if there are 500 content databases in your farm, you will need at least 5 query servers.
Web server/database server ratio	8 Web servers per database server	The scale out factor is dependent upon the mix of operations.
Web server/domain controller ratio	3 Web servers per domain controller	Depending on how much authentication traffic is generated, your environment may support a greater number of Web servers per domain controller.

Performance Guidlines

This table shows the guidelines for the acceptable user response for four types of user operations:

Type of operation	Examples	Acceptable user response time
Common operation	Browsing to the home page Browsing to a document library	<3 seconds
Uncommon operation	Creating a subsite Creating a list	<5 seconds
Rare operation	Backing up a site Creating a site collection	<7 seconds
Long-running operation	Indexing a site	Varies with operation and system configuration. All long-running operations will have either an information or status page.