Recommended number of Project/SharePoint Workspace

A partner recently asked me the following question:

Is there a recommended limit on how many workspaces can be created at one level?

First please refer to the following SharePoint documentation on TechNet: Plan for software boundaries (Windows SharePoint Services)

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.
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

Blog posts on the same subject:

Secondly, a work around is to use SQL Server Reporting Services to filter out the list based on custom fields: http://blogs.msdn.com/chrisfie/archive/2007/10/03/controlling-the-project-workspaces-list.aspx