I just updated my mid 2011 MacBook Air to Yosemite and it feels a lot like how iOS 7 was in beta form (not that I'm whining about it. I know it'll get better as new betas come out). My biggest problem is that Handoff isn't working. I turned it on in settings but it doesn't seem to work. It's working between my iPhone 5C and iPad Mini with iOS 8 but not between my MacBook Air and my iOS 8 devices.