:roll: Stop listening to retarded rumors, guys (or trusting the garbage "application compatibility" features), and just test stuff out by YOURSELF. I use Win8.1, I have 0 issues with my mouse (Logitech G400s, using latest Logitech's software) or with CS:S and CS:GO and I don't personally know anyone who does.
When the maker of the OS and/or the games in question post that there are potential issues, that's a bit more than "rumors". And, the reason I asked at this website is because a lot of folks here 1.) are gamers; and 2.) are pretty aware of issues that revolve around current upgrades. Personally, I'd rather take the few minutes
to ask around and do some research than waste a few hours
doing the upgrade and troubleshooting problems, only to waste even more time reverting back.