I have MSVC 2008 and 2010 installed.
Now I've tried to build a project using a Qt built with VS2008.
Running it crashed immediately because Qt Creator built it with VS2010.
I observably aged while looking for the reason for this crash.
Building a program with VS2010 and linking VS2008 libs is deadly.
Qt Creator should deduce the right toolchain from the chosen Qt.
It might do this by looking at the mkspec.