Some tools for troubleshooting SharePoint 2010 performance
1) Turn on SharePoint 2010 Developer Dashboard. It will reveal why a page takes so long to load.
http://sharepoint.microsoft.com/Blogs/GetThePoint/Lists/Posts/Post.aspx?ID=457
2) Use perfmon with the following recommended performance counters
http://technet.microsoft.com/en-us/library/ff758658.aspx
3) Read and analyse performance data
SPDiag 3.0 - http://technet.microsoft.com/en-us/library/hh144782.aspx
4) What to do with the results?
References of Real life performance testing.
Microsoft's perf & capacity test results and recommendations
http://technet.microsoft.com/en-us/library/ff608068.aspx
Side track -
This tool is not specific to SharePoint, but it does have some threshold & help analyse data from Performance Counters
http://pal.codeplex.com/
