I bought my rMBP on 16 september, 2014. 2.6 GHz, 16 RAM, 256 SSD. When i was running mavericks on macbook it was fine, but ever since i updated to yosemite. I noticed lags in mission control and switching between windows. I have to use " reduce transparency" to make it less annoying. I've try reset PRAM, it works for a while and then thing gets slow again. I don't know if it's just me, but i'm really disappointed. I spent money on thin machine and this is not what i expected. Is this a hardware issue or just software issue? cause one of friend brought a base model and it worked really smooth.