I've upgraded my mac from Mavericks to official Yosemite. In the first day my mac was normally, but in the second day, it was unusable, very slow and it was not responding, The third day(now) still like that. I dont know what to do, I've already reset pram, reset smc, repaired disk permissions, tried to reinstall Yosemite and nothing changed. I think it can be the file vault that I had activated when I upgraded to Yosemite, but I can't even know the percentage of the process. My MacbookPro is a version late 2011, processor i5 2.4Ghz, 16gb ram, 500gb HD. I would appreciate if somebody could help me.
It seems to be a common issue with Yosemite, see e.g. a Mac Rumors thread.
In the last couple of days there also popped up several articles complaining about Apple’s current state of its software. You can find a good overview of the most common issues in this article (it’s also worth to skim over the comments as there are issues that aren’t discussed in the article).