Major advantages to iMovie vs. the Flip software: Ability to add titles, subtitles (though I didn't do that this time), music, change music levels, and eventually use all the other iMovie capabilities.
Rendering time was much faster (though the YouTube processing still takes a while; not done as of this writing).
Upload time was much, MUCH faster: Even though the file was almost three times larger, the upload took five or six minutes vs. around 45 min.
Major disadvantages: File size much larger, though I don't know how much this was because of titles and music tweaking. Also, the Flip software let you share it with the Flip site with the push of one button (but upload takes about 45 min. for less than 3 min. of video for their site as well as for YouTube).
Lessons learned, after two videos: 1) I should use a tripod. A small tripod will be part of my convention kit, and I should have lugged the larger one on this journey. 2) It will take too much time to make complete videos during conventions. I'll probably have to stick with the simplest recordings. Timely videos will probably be instead of timely snapshots. Unless I do something drastic and get a laptop...