I've also noticed VSTS (SP1) perf. go to heck with the add-in. Memory usage goes to almost 1 GIG (972,000K, normally about 280,000K) and I spend most of my day waiting on machine...processor and hard-drive rarely stops.
This is a *very* large project so perhaps it's trying to constantly compile things? Normal compile takes about 2-3 minutes as is.
This is a C# solution (13 project - 6 class, 1 web, 1 databse projects, 5 test projects).
After disabling add-in for productivity and restarting VSTS everything is back to normal.