I've been using Vista for the past 2 weeks on my new PC. I also have Vista on my laptop that I got for school. In both cases I didn't have a choice considering HP wouldn't offer me XP for either of the models I wanted, and I didn't want to go through the process of reformatting them and installing XP.
What new features does Vista have? I... Don't know. After two weeks, the only new feature that I've found is the ability to search within a folder, which is nice, I guess. You're going to have to relearn how to do some things that you know how to do on XP, but it's not that bad. If you're going to be doing a lot of gaming, just know that as of right now, games generally work better on XP. For example, on some game boxes, you'll see system requirements listed as needing 1 Gig of ram recommended for XP, 2 for Vista (ie: assassins creed. Pretty sure this is also the case for Mass Effect).
My laptop used to crash a lot. I'm going to go ahead and blame this crashing on Vista since after SP1, the amount of crashes went down drastically, though it still occasionally crashes.
The last thing I can think of is that I think some hardware / software isn't 100 percent vista compatible, yet. I personally haven't run into any of that, my desktop works just fine as does my printer and all of that.
But uh, good time to upgrade? I personally don't think it matters either way. I was under the impression Microsoft was releasing another version of Windows in like three years, though.
The best compliment I can pay to Vista is that I don't think I mind not having XP installed, I'm indifferent to both of them. There were some occasional moments where Vista pissed me off, but nothing major. I just want to end this post with saying **** the 5000 confirmations required when you're installing anything on Vista.