For a start, Server 2008 = Vista, and Server 2008 R2 = Windows 7.
But yes, while in theory it's very possible (And you've even got things like the Desktop Experience feature) and many applications will work great many will also not. Some applications just don't like Server Operating Systems - whether through a deliberate attempt to distinguish between home and corporate users, or just through incompatibility or security issues.
The problem is, by the time you've server you're 2008 box into a workstation, you may aswell be....using a workstation.
So, I think the bigger question is - what do you think you're going to get better from Server 2008 (or R2) over Windows 7?