I noticed the same thing with my daughter's digital camera which saves
to .mov format. The movies play very slowly, and skip frames. After I
converted them to avi they play fine. The camera I got saves to avi
format and the movies from that camera play as expected.

Not sure if this is an ubuntu issue, I'll have to try on some other
distros when I get a chance, but I'm guessing there is a less than
optimal quicktime codec involved.