On my mid-2011 iMac I have also found Yosemite to be snappier. I hardly ever shutdown my computer, but obviously had to restart it 2-3 times since updating (unrelated to the OS directly - other software upgrades that required a restart). The startup time on Yosemite is much better than on Mavericks (for me, at least), and I haven't had any negative experiences so far. Apps seem to open much faster too.
My husband has a rMBP, but he hasn't used it enough since updating to comment on battery life, etc. - though he has experienced the WiFi issue some have complained about; nothing too serious for him, based on his current infrequent use.