I hate having to reinstall my OS, and I avoid it as much as possible. While I agree a fresh install typically performs way better..I hate having to setup everything, tweak everything, get it all perfect again.

I run OS X and in the three years I've run it, I've never once had to reinstall the OS. Not to say that it wouldn't hurt, but I've never even felt close to needing to do it.

Before OS X (and still on the family computer), there is an install of XP that has maybe been reinstalled 3 times (over 5 or so years) and only when it's absolutly needed. The only reason for it is my family does not know how to keep a system free of sludge, you know? But is it really their fault? That's my question, should it be up to the user to keep his/her system clean? Or should it just be safe anyway (without sounding like an advertisment, like Mac OS X) ?