Honestly, I'd second that last comment.
Win7 is a nice upgrade from WinXP, but the difference between Vista and Win7 is minor.
I'd held onto an upgrade copy of Vista for years (it was provided to me as an upgrade to my last purchase of WinXP Media Center Edition). It wasn't until I'd used the pre-release version of Win7 for several months that I decided to install Vista.
Frankly, I'm glad I did. The negative publicity Vista has received has really impacted what I feel is a pretty good OS. Those security pop-ups Apple went to so much trouble to make fun of in their ads? Hey, I appreciate Microsoft's intent with these. Better that I should be notified, than to allow a third part package (potentially carrying malware) to be installed on my system.
Overall, I don't see enough difference to justify the move from Vista to Win 7. They both use the Aero interface and both support DirectX 10 and 11. In the future, Internet Explorer 9 will run on both platforms, as will any other software.
So, why would you want to upgrade Vista to Win7? There are no compelling advantages to it.