Sharepoint 2007 Guidelines

object	Guidelines for acceptable performance	Notes	Scope of impact when performance degrades
Site collection	50,000 per Web application	Total farm throughput degrades as the number of site collections increases.	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.	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 library4,096 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