As a TFS admin I sometime wonder how many team projects is in use and maybe when it was last changed. Sometimes I've been forced to find out and I have created some SQL queries to run against the warehouse to figure it out.
Packaged into an custom SSRS Report
Now I have packaged those queries into a custom SSRS report for tfs2008. You download the report at my skydrive http://cid-5d46cae8c0008cf0.skydrive.live.com/self.aspx/.Public/TeamProjectLastChanged.rdl Once downloaded you simply needs to upload it to your own TFS Server and point the data source to the tfs standard TFSReportDs shared data source.
TFS2010 updated version http://cid-5d46cae8c0008cf0.office.live.com/self.aspx/.Public/TeamProjectLastChanged2010.rdl