Call me the guinea pig of the team, but I'm using Vista Ultimate right now. Like people said, there are issues. Most I assume are caused by my somewhat-old computer. I've had WMP crash several times, but I don't use it often anymore. The start menu -> All Programs likes to lag a few seconds. Preferred XP's style.

BOINC runs fine as well as most of my games, so backwards-compatiblity is good. Some games crash for the craziest reasons (ex. Changing video settings).

The ATI drivers could be better, I can view BOINC graphics and they'll be like 2FPS while they were smooth before. Games are somewhat laggier too.

We are all not a fan of DRM, but I don't have any HD movies or hardware so I can't comment on that.

I'm sure Vista will improve over time. But I've heard MS is already working on the next-gen Windows "Vienna" set for 2009, which doesn't seem to leave much time for Vista to become mainstream like XP did. But we'll see in the future.