Each to thier own I suppose and I have had no dealings with XP (most I've done with XP is install XP home and more or less take it straight back off again) where the SPs sound so big but I've done quite a few Win2K pro reinstalls.

My preference is generally to reinstall. I will normally have a quick play and look through the MS KB etc. and if things fix more or less straight away fine but I have known several people, myself included, waste far more than a weekend trying to troubleshoot windows, follow KB articles that describe the problem but don't fix it, etc. so my opinion is it can often be quicker just to reinstall and have done, plus have the knowledge the system is clean again.

As for remembering what programs need reinstalling, I take the view if I can't remember a program, it probably has no business being on the machine any longer anyway.