I went out to try and catch a timelapse of the meteor shower last night. Didn't catch too many, but ended up with a pretty cool timelapse of the sky. An interesting issue I ran into = even at 800 ISO, the GH2 was showing horrible, big thick bands of color noise across the frame with long exposures. They would move around between frames and it made shooting a timelapse with it impossible.
After some poking around I realized what was causing this was the GH2's long exposure noise reduction setting being set to ON. After switching it off the bands completely disappeared. Of course now you can see you get some really hot stuck white pixels in your shot. Overall I'm very disappointed in the GH2's low light performance. I used to shoot 20 second exposures with my 5 year old Pentax DSLR and never once saw a stuck pixel, or big bands of noise, especially at 800 ISO. And yes, I did a pixel refresh in camera before shooting. And yes, the banding from the noise reduction set to on is present in RAW, and it's ugly.
Result below (I highly recommend switching to HD and entering fullscreen to be able to see the whole starfield)