SharePoint 2007 Limit/Guidelines

Here are some guideline for site objects

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	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
	4,096 per list
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

Here are some guideline for search objects:

Search object	Guidelines for acceptable performance	Notes
Search indexes	One per SSP	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.
Maximum of 20 per farm	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.

Some architecture guidelines:

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

Source: http://technet.microsoft.com/en-us/library/cc262787.aspx