I feel like I'm taking crazy pills, as Yosemite has been the best OS X release since Snow Leopard for me. Runs brilliantly, added a lot of nice features (Continuity and nicer widgets than Dashboard), looks better than Mavericks (and much better than Lion or ML). Then again, I use a MacBook Air, which doesn't usually seem to be the Mac of choice for people on here, so... shrug
Sometimes the mouse still moves, but nothing else. About 50% of these cases I need to reboot the laptop. I used to reboot my Mac once a month or less. Now it's daily.
I want to downgrade OSX from 10.10 to 10.8, two versions back, because I read somewhere that it's the fastest of them.
In the last 2-3 years, Apple only added self-serving cloud shit and tried to make everything more like iOS, but the fucking Finder columns still don't auto-resize to the length required to read the filenames without "...." in the middle.