Earlier versions of the beta didn't have that problem. I think it was beta 3 when it showed up (out of 6). I reported it a couple of times during beta testing but it was never fixed. This on a 2010 Mac Pro with Yosemite installed to an erased drive so any such problems cannot be contributed to installing over an older OS.
Where I see it most is opening folder windows. Instead of smoothly expanding to the open position, they stutter across the screen, showing multiple partly drawn rectangles up to the point where it stops, then cleans up what was supposed to be the genie effect. After doing any given folder once, and you then close it, that folder will open in the smooth animated style as it's supposed to.
It also affects some older apps I have. They draw very fast in Mavericks or older, but on the same hardware, these apps draw very slowly in Yosemite. Something they didn't do in the earlier beta releases.
Something wrong was done to the graphics drivers somewhere around beta 3 that needs to be fixed. Likely only affects some model Macs as it's not an issue that is being widely reported.