@Cameraman, we're all still waiting for a good slow/720p patch. @Driftwood has a 1080p 80% patch that could work as described by @arvidtp above found hear
http://www.personal-view.com/talks/discussion/1002/official-low-gop-topic-series-2/p15
and also he did some 720 50p/60p patches but they are not very stable at least for the 60p. Both 720p patches are also found on the above like, just read back I think to like page 9. Good luck, I have being looking for the best way to get this especially as I have some shoot coming up this weekend where I will need some slow mo.

@cameraman I've also tried various patches and settings in attempt to achieve good slow motion in full hd on the GH1, but from my understanding the sensor captures the image as 24p and then wraps it into 60i which plays back at 29.97 on your computer.

Trying different de-interlacing methods from the 60i footage I've come to the conclusion that getting any motion information above 24p (or 25p in PAL) is not possible. Even though the file says 29.97 it's only 24p with extra frames, which is noticeable when you skip through the frames one by one, where you will notice that some skips does not change the frame.

As far as wrapping and sensor output of the GH2, I dont know.

So I think your best bet for filming fast moving objects is going with 720p. If you film something less extreme, say a person walking in normal speed you could probably do it in 1080p and use twixtor or similar program to slow it down (remember to use high shutter, twixtor does not cope all that well with too much motion blur).