I'm planning a follow-up article on preparing movies for playback on gMovie Player, but have a couple notes to share right now for those playing with the demo version.
I think it's best to keep your audio tracks simple and avoid to many "high notes." If you "normalize" the audio before converting with gMovie Maker, this seems to help too.
Generally speaking, drums do better than horns though ;-)
Also, you are limited to 20 seconds of video on the demo version, so you may want to edit down your clips in QuickTime Pro before converting with gMovie Maker.
Finally, I did more testing on beaming video last night, and was surprised at the performance. A 240k clip completely transferred from a Visor Prism to a Visor Platinum in 50 seconds. That makes sharing clips a practical reality.