So far I have found that Nero'sShowtime media player plays back Sony format HDVV M2T files far better than any other media player. Select the "bob" deinterlace method from the options menu and prepare to be amazed. On my system, there is a small glitch about a second into playback, but aside from that, it's the smoothest HDV playback I've seen.

Now all I need is a media player that will playback Cineform files smoothly. So far I can't find one.