I own a rMBP 2013. On the Yosemite GM candidate turning off transparency (found in the accessibility section of settings) increases 2D UI performance by quite a lot in certain areas. I'm hoping this will not be the case with the final version but looking at what happened with iOS I wouldn't put my hopes up. The same can be seen in iOS 7 and above. Disabling it makes certain things smoother. Even on my iPad Air, which isn't really old. This post on reddit was at the top of /r/apple. Inside you'll find people with different devices stating that this increases UI performance. We've been moved into world where driving 3 million pixels and above is considered normal. Apple had a huge part in this and I am thankful (although GPUs everywhere aren't ), but why include something that puts an even greater stress on already somewhat stressed products. Also if anyone knows why transparency makes things a bit slow that would be great. Did it do the same on windows Visa or whatever version it was? Is it just inherent to using this effect or is it that way that it's implemented by Apple?