I recently upgraded my 2011 MacBook Pro to the new OS X v. 10.10.x or as most Mac users now it...YOSEMITE. Up to this point I have thoroughly enjoyed all of the subtle and not so subtle improvements. For a brief rundown of all things new in Yosemite, click this link or go to Apple.com for a Yosemite description.
However, I have found one major issue (a known bug) with it and according to many support sites and forums, it has affected several Yosemite users. Depending on my location, the wifi connection will just suddenly turn off. That's right...I'm connected and then not connected. Simplest remedy is to turn wifi off and then turn it back on but I found that only lasts a short amount of time. For a more long term solution (at least until Apple fixes it) click this link. I have found this solution to be much more stable and long term...although occasionally it still will lose connectivity but with much less frequency. C'mon Apple...you're better than this ;-)