I usually do a spring and winter deeeeep cleanup of my netbook... I mean... Deeeeeeeeeep!
I tear it apart bit by bit... Then, after hardware cleanup, I reassemble the bits...strangely there's always a screw that seems to have no were to go... Then I clean the system... Byte by byte... Full low level format!
Typically a 2 days endeavour!!
@Cableguy it seems that I find that we are more alike every time you post a bit about yourself. I tend to strip my system(s) apart about every 18 months (all screws accounted for though, I'm an engineer after all! ). My laptop and desktop usually have the OS reinstalled although I don't do that with the Server, just a deep clean is sufficient for that. But then my desktop and server both run 24-7 so they build up quite a bit of dust.
I've started to do a fresh OS install along with drivers, apps etc then take an image of the setup system...easier and quicker to do a fresh install. If all your data is on a different partition to the OS it's even easier.
A lot of the cheap keys being sold for Windows are from volume licensing and are not supposed to be resold.