I am having a problem in Premiere Pro CS5 (fully updated) where the playback (in the program monitor and source monitor) is always choppy when viewing AVCHD footage. It appears that the video has a "twitch" about once per second. My footage is coming from a Sony NEX-FS700, 59.94, 1280x720. I believe that my Premier project / sequence settings are correct.
I am running Mac 10.8.2 on a 2.3GHZ i7 w/ 16GB of RAM. It is a retina display.
The only time that I have seen something similar, is with Flash's use of Hardware Acceleration. I had to turn off Hardware Acceleration in order to get a few streaming videos to not be choppy/twitchy.