"If you are deploying SharePoint, you really need to load test the servers before putting them into production to make sure you've sized your servers properly."  That statement about says it all.

The MOSS perf team has released sample web tests and load tests for testing Windows SharePoint Services, Office SharePoint Server, and Excel Server on CodePlex, at http://www.codeplex.com/sptdatapop 

 

Ed Glas's blog on VSTS load testing : SharePoint Load Tests