I've had 2 of my ISV buddies ask me this, so I'll provide the link here that I have to them: 

   http://msdn.microsoft.com/netframework/programming/breakingchanges/default.aspx

On a fully-unrelated note, as Buck mentioned, the TFS Beta3 VPC image (with all 3 tiers on the one machine, so give your VPC lots of memory!) is done and should be on MSDN Real Soon Now!