I asked previously if there are good reasons to partition disks on Windows, and one of the big ones was for splitting data and OS. So that should you reinstall, you do not need to worry about the data (i.e. the partition with the OS gets wiped, while the data one remains).
Windows 7 allows you to have a VHD (virtual hard drive) file as a drive in the OS natively. My thinking is that you now have one partition and you create a VHD with the data on it. That way moving from machine to machine or reinstalling you just need a copy of the VHD. You could have two partitions still and dedicate one for the VHD, which gives a best of both scenario.
Is there any pitfalls or issues that could occur in this scenario?