Yes, I'm thinking of getting the sony media converter to do the same thing. Unfortunately the conversion to MPEG1 is terribly slow. Even expensive software like MediaCleaner is really slow too. Heuris makes a plug-in for iMovie (or FCP, can't remember)but I doubt it's any faster.
Your PB processor and RAM might make a difference though. From what I know, a 70-80min movie takes 4to6 hrs. to decode on a fairly fast G4.As for hardware decoders, I'd imagine they're too expensive and probably would convert form DV.
Hope I could help.