Eweek.com has a great article about why Windows Vista is so bad: Night of the Living Vista.

Opinion: Vista has turned into the desktop operating system no one wants, and even Microsoft is beginning to get it.

Today, I think of Vista as the zombie operating system. It stumbles around, and from a distance you might think it's alive, but close up it's the walking dead.

[...]

There are many reasons why Vista is doing the zombie stumble. Microsoft has and continues to mislead customers about how much PC is really needed to run Vista. Even some of Windows' most loyal users are finding that its poor performance, lousy software support and pathetic driver support is too much to stomach. People who wouldn't touch any Microsoft product until the first service patch appears. And, last but never ever least, if XP isn't broke, why "fix" it with Vista?

[...]

If you want a better operating system than XP, may I recommend Xandros as the most painless way for an XP user to give Linux a try, or if the idea of installing Linux gives you hives, you can just buy an Ubuntu-powered Dell 1420 laptop, which is a very sweet machine. Or just bite the bullet and go ahead and buy, say, the new MacBook Pro 15-inch to give Mac OS a try.

Whatever you do, even if it's just sticking with XP, you'll be doing better than moving to Vista. Vista is the walking dead of the operating-system world.