At my current client, I'm using Visual Studio 2010 inside a VM and the overall experience was, well...excruciating. Turns out that VS uses the GPU to help rendering the designers, IntelliSense, etc. Well, since a VM provides a software video card, the result is a painfully slow experience. A quick search lead me to this Code Project tip and the solution is shockingly quite simple: just disable hardware acceleration in the VS settings!
In the Visual Experience section: uncheck "Automatically adjust..." and "Use graphics hardware acceleration..."
Your mileage may vary.