Why is everyone so keen to reformat?
Put a fresh build on the same disk if you're so determined to spring-clean. You get all the same benefits (some of them rather dubious in my mind), but:
1. No need to back up your old data (although it's good practice to do so);
2. Profiles can be copied across. Why waste time setting up the UI
just how you like it, all over again? And you have
got written copies of all those passwords that Windows currently remembers on your behalf, right?
3. Saves lots of time;
4. Removes the risk of losing anything that your backup round missed!
5. If you habitually keep a local copy of any patches, retaining your old partition will also save you some very
long downloads - and it's nice to have a machine that's secure before you even connect to the internet for the first time, isn't it?
6. Lower stress levels; if anything goes wrong, you can boot back into the old OS
. Don't know why your internet connection won't work on the build? You can use the old one to connect and look up the answer / get an updated driver / whatever.
There are probably more, but I'm not ranting coherently...