I have 3 macs, all fairly current (2.8 Ghz 2008 iMac, 2.4 Ghz 2008 MBP, 2009 Mac Mini). Not one of them can play back video in any format that doesn't have at least minor constant stuttering. It doesn't matter what the format or source is (H264, DV, HULU, YouTube, DVD, eyeTV etc). It doesn't matter if it's full screen or windows. It's about the same for all formats on all 3 machines. It doesn't matter if the source is local or network. It's most noticeable when there's a slow pan shot there's always a random jerkiness to it. Framerate will be smooth for a second or two and then a random jitter. My playstation3 can play stuff recorded with eyetv streamed via medialink and its 100% smooth, but I bought the Mini to use as a media center. Playing the canvas out FireWire monitoring in FCE is perfectly smooth. I would have hoped we were beyond the era of bad computer video playback by now.