Well, I'm on ME, and have had no troubles with it. And since upgrading OSes can do evil things if you don't pop Nev's FDisk, I'm in no hurry to put XP on my laptop.
On my older comp, I'm sticking with 98se. It's loaded with quirks, and lives to crash, but I've heard of many problems with XP and older programs...and new ones too. I still play DOS games (DooM rocks!) and I don't want to lose it. Also, a friend on XP has had a few dozen hardware problems with it, mostly driver conflicts.
That, and I hate the Mac-esque interface and proliferation of "Wizards". I dont' want gradient colors and bubble textures eating my desktop. I want everything at once and more.