It happens to me at least once a week, if I'm doing a lot of debugging performance analysis, it can happen once an hour.
I've put this little section in a batch file and whenever it happens, I just click it and my problems go away.
It kills the performance analysis and the ASP.NET Development Servers processes.
You'll need to install pskill for it to work.
pskill WebDev.WebServer40.EXE pskill WebDev.WebServer20.EXE pskill WebDev.WebServer.EXE pskill VSPerfMon.exe