Upgrade is a lousy idea. Clean install is the way to go, upgrade is just a catch-phrase. As in "upgrade from Vista". Isn't there a price difference between the full version and the upgrade version?
edit - Yep there is a price difference. Many will go with the upgrade version to save money.
The asking price is not worth the aggravation in my opinion.
I will stick with slow and highly Bloated Windows Vista.
No aggravation at all. I did two installs last last night with Win7 64 bit. One on a laptop and one on a desktop. it went very smoothly.