For entertainment purposes, I imaged my C: of my home computer (safety first!) and did an inplace upgrade yesterday.

Flawless.

The only program that I have had to reinstall so far for some reason... Office2013. Didn't have to download a single driver or update either. Every game I had installed on the machine ran without a hitch.... and with less hitches (easily picked up 5-10fps in GTA5 but more investigation is required). My mysterious rhythmic stutter in GTA5 is gone though, so that's awesome.

I had originally planned to follow through with a clean install regardless of the results here... but I'm really not seeing a reason to right now.