In addition to a scenario that I described yesterday (TypeMock 6.x) causes build on build machine hang, a combination of TypeMock and TestDriven on a local development machine also occasionally hung after executing all tests. The only way to go forward was to kill ProcessInvocation.exe.
Interestingly, the problem went away when I installed latest beta of TestDriven.NET (3.0 beta 2). Still, since there's been several reports about Isolator 6.0 behavior in combination with other products, I believe the issue has something to do with Isolator (I've been successfully using TestDriven.NET 2.24 for a long time).