I'm triple-booting Vista, Ubuntu, and XP right now, but Vista is the primary OS I use on a daily basis. Why? It's Nvidia's fault. A little while back they introduced SLI multi-monitor support, which is a feature I've wanted for a while, but it's ONLY for Vista.
Running XP is going to continue to be viable for a while, just like Windows 98 was for a while when XP came out. But eventually, new products or features are going to come out from third-party manufacturers who didn't/can't invest the time and resources developing for a legacy operating systems. And if you want access to those products or features, it may eventually force you to upgrade.
Personally, I find Vista's user interface to be a step backward for Microsoft, but over time I've adjusted to it and it doesn't much bother me anymore. Yes, it's bloated, but performance issues aren't noticeable on newer machines - as long as you have at least 2GB of ram and a fast enough processor. And games, well, they DO look really nice using DirectX 10.
I'm definitely hoping that Windows 7 will improve on it, and I intend to replace Vista as soon as it is released. I've been reluctant to try the Beta or Release Candidate because I can't afford to have an unstable operating system. Let others work out the bugs, I say!