I got my Lumix GH1 recently, shot this test with it the next day; never touched one before. Threw it together with some music in Final Cut Pro, quick color work in Magic Bullet Looks, and on to the Vimeo.
Used the stock lens and a Nikon 50mm (f1.4.) I had to shoot most of the stuff at fast shutter because I have no NDs yet. Managed to catch myself in a few reflections too. Tried for a variety of shots.
Shot 720/60p. Haven't noticed any banding or macroblocking ("mud") problems really. There is a bit of fuzziness in the water-spray, aggravated by web compression, I think it would have been better at a slower shutter but that was not an option.
Shot with lowered sat, contrast, and noise reduction, to boost my leeway in post.
The camera was a joy to shoot with; this shoot took about an hour total, maybe less--much easier to deal with than a shoot I had about a week back using HVX-200 + Letus.
Song is "Happiness" by Kasabian, off their new album "West Ryder Pauper Lunatic Asylum."
Let me know what you think or if you have any questions!