I also lack any reason to leave good old faithful Win2K, except that I also had to revert to CB_20070308. I have XP on a laptop since it was preloaded. Other than that, following any hardware upgrade, 2K goes right back on my desktop. No activation required either (thanks a lot Vista!) and everything just works.
Now of course, if software support disappears for it then I will have little choice. I won't even have a choice to upgrade to XP since MS is taking it off the shelves. So it will have to be either Vista, uugh, or a move to Mac or Linux. I hope CB will continue to support 2K for as long as possible.