This is a bit off-topic but I wanted to share because it seems a lot of people are running into issues with choppy video playback and stutter on Mac OS X.
I am using a Mac Mini with Snow Leopard (10.6.8) as a home media center and it has worked great in the past, playing back music and videos from multiple sources (web, quicktime, VLC, EyeTV). A few weeks ago the video playback from all my sources started to become choppy, to stutter, and often the picture would hang for seconds at a time. Totally unusable. Drove me nuts for two weeks.
After much research and trial-and-error it turns out the problem was an outdated Flash Player which seems to have messed up the video pipeline for the entire system. The short is, I updated the Flash Player to version 11 directly from the Adobe web site, rebooted the Mac Mini, and all is well again!
Judging from the various posts across the web, video playback appears to be a fairly widespread problem for Mac users and I hope this helps some of you out there! And I can’t wait to get rid of Flash altogether – I can’t remember the times it has crashed my browser, hung my system, and screwed up things. Thanks Adobe ;-(