If you use Mavericks and then Yosemite the difference is as clear as day and night. Mavericks was one of the most stable OSes I've ever used -- on the same level for reliability as Linux! Yosemite, however, is worse than Windows Vista. I've had such a bad time using it that I'm considering switching to Linux or even Windows 10 (for work). The honesty is after multiple kernel panics and daily lockups of the system, I can't handle how bad it's gotten. I didn't want to admit it... Apple is where Microsoft was.