No matter how much housekeeping you put into your OS, you'll eventually need to rebuild. I’ve used every tool under the sun to optimise the registry, keep things in check. The majority of these tools are just additional bloatware and do the opposite of what’s advertised. I think it’s fair to get a good year of of your OS then it’s time to rebuild. To find out when your OS was installed type ‘systeminfo’ at the cmd prompt. This will show you the build date, how long it’s been up and a few other useless things.

Cheers
Ryan Partington