I've also not upgraded and am still using XP Pro. I do have Vista on a laptop, as does my wife, and I hate it. It is definitely not designed to work well on laptops and just feels slow, bloated, and clumsy. A well configured XP is much nicer. Although the funny thing is I used to say exactly the same thing about XP when I was using 2000 as my main OS.

I think it has more to do with hardware reaching a point where is can run a version of an OS without any problems. When a new version comes out the increased resources needed is always bad to begin with. But a couple of years later when graphics cards, CPU power and the amount of ram has grown that all changes.