Won't get too many replies in this topic.
I was under the assumption that the new hacked 1080P on the GF1 was nothing but the 720 MJPEG on steroids. Oh well, I don't have one, so what do I know? I do have a hacked GH1 though.
I was having some problems trying to make the bitrate around 100MBps in MJPEG (lots of card and camera crashes, probably more card related, however), but now I've settled on 32MBps 1080/24p AVCHD. I've used the settings for more than a week without any problems.
I did have it at 44MBps shooting AVCHD (which was stable also), but I figured it would probably be a whole lot wiser to have fully-stability with my cards and camera than have the best quality with a crash at the 40th minute or something (need to pick up Class 10s). I'm still waiting for all the dust to settle though. Once it does, then I'm sure we'll all know the optimal hack settings for both cameras. Besides, you can always reset it when things go sour.