I must say I've not had a negative error number... or any obscure error in MacOS X, so far it's the most stable OS I've used... but then I don't do anything weird, just running a few professional apps (notably Logic Pro 7.2) and general computer use (Internet, Email, M$ Office etc...).
Windows XP, is a pretty good OS... but I've never had a Windows installation that hasn't needed a complete reinstall after about 12 to 18 Months... WinXP SP2 is sofar proving to be rather good though! Not stable enough for live music work though.
But for mission critical stuff, I stick to MacOS X.