I have noticed that with Yosemite GM3, WindowServer seems to be taking up around 30% - 60% CPU (depending on the number of open programs) whenever UI transparency is enabled. I didn't notice this kind of behavior in Mavericks. Turning off transparency drops it to around 8% but it was usually less than 1% in Mavericks. This is on a Mac Pro with D700s, it doesn't happen on my Macbook Air with Intel HD 5000 graphics. Can anyone else confirm this?