simply doing "rate -1." will play it backwards at normal speed. I’ve found that using tons of "frame $1" messages can play back less smoothly, and I’m not sure how well the audio tracks along. The audio can also be a problem when doing lots of rate changes, especially backwards…the video is always fine, but the re-processing of audio that QT tries to do can slow things down and sound funky.
If you don’t have any audio in the movie, you’ll be totally fine :)
(note that this is different than having an audio track and saying "vol 0.")