Another possible gotcha... is ODBC / DSN setups if doing 64 Bit.

Windows x64: 32bit Odbc vs 64bit Odbc

If you do decide to go Vista 64 Bit then you might want to review a bit from sites like this: vistax64.com

I suppose the issue is, do you want or are you ready to have to potentially fight issues as they come up. I tried to use 64 Bit Server 2008 but after just one day I gave up as there were too many obstacles and old software or methods that I just was not ready to Update/Fix/Study/Etc.. at least right now. If I had a second box to play with in my spare time maybe, but not my main system.

As an example none of the Cisco VPN clients work with 64 Bit but they do have another method of a client that does work on 64 Bit but it's not a click install so I just didn't want to spend the time right now to read up on it and configure it to work.

The good side of using Vista either 32 Bit or 64 Bit is that it will increase your knowledge level as you will be forced to learn new things whether you want to or not.