I started using the GH1 2 years ago and since 1 year I'm shooting with two GH2s. I think it's the best video-cam ever and audio is excellent too. The video on top of this page was shot with two GH2s:
http://www.femanic.com The colors didn't come out the way I wanted, and my color correction skills aren't good enough yet, but the basic video image is great. If you scroll a bit down, the video with Jolanda and Daisy was shot with the GH1.
This site has great info about movie making with GH2 and other DSLR cams but the GH2 absolutely is this guy's favorite cam too:
http://www.eoshd.com
I can't tell you anything about the G3.