A couple of my buddies and I have been running Vista for quite sometime now, pretty much since it's release. I have been running it since Beta 1 and have had very good success (I am now running Ultimate 32bit and my buddies are running Home Premium). I ran into the first and only app so far earlier this week that gave me a little bit of grief. Command and Conquer 3 (which is amazing by the way) won't let you run unless you create a NEW account on the system with local admin rights. Even with UAC turned off and your existing account added to the local admin group, the app will puke at a certain point. I'm sure it's just a permission issue, but I’m too lazy to audit the system and find the source. The easy work around was to create a local admin account and then modify the C & C shortcut to do a "runas" with the newly created account - that way I don't have to log on and off. ALL Steam games that I play (HL:2, CS:S, DoD, DoD:S, Garys Mod, etc.) work GREAT without any noticable performance hit.
Bottom line - there is very little that Vista has to offer over XP other than heightened security and a very stunning visual interface (dreamscene is orgasmic). There are a few minor things that are nice to have, but nothing stellar. Of course, there is always DX10 support which will become more and more important and the Vista Media Center is WAY better than Media Center 2005.
Also note that most of the complaints you here from people about Vista are from two types of people – 1. People who aren’t actually running Vista or tried it for 30 seconds before deciding it sucked (it’s different, it will take some time to get used to). or 2. People who have junk hardware and are upset that Vista slows their system down or that there aren’t drivers for their off-brand sound card. If I hear one more person say "Vista sucks! It's so slow on my Celeron 2.4 w/128MB of RAM!" I'm going to scream.
If you have any Vista questions Outbreak – feel free to PM me.