The most serious bug I know of it the registration process in XP and the unfair monitoring of changes made to the system.
That's a bug that I will not have in my OS.
Therefore you wouldn't catch me dead or alive with XP on my computer.
If I spend my hard earned money on an OS, it's not going to shut me down because I love to make many system changes, and low level format my drives.
There's bugs alright, but Bill Gates don't call it a bug.
Too bad.