I'm having one issue with Yosemite, which I've mentioned here before -- Instant Hotspot between my 2012 MBP and my iOS devices is difficult to connect (between iOS devices, no problem at all). This *could* just be me, though. Other than that, I've found Yosemite to be much better than I initially expected. Really looking forward to the finished El Capitan (but to echo what I just wrote in another thread, AVOID this public beta initial release unless you are serious about working with beta software!).