Just picked up a Panasonic ZS3 and I am experiencing the fast playback issue with iIMovie '08.
Apple Acknowledges the issue - see link:
http://support.apple.com/kb/HT3481
This website was updated June 09. Workaround is to upgrade to imovie '09.
I think before I upgrade I am going to check out the Canon SX200 IS and see if their codec has the same issue in imovie '08.
From reviews I read, Canon has more manual features vs. Panasonic, however, when shooting video I believe the Canon can only go up to 4x optical zoom.