There is a long and incredibly interesting thread in the dvxuser.com forum where people analyze the video quality of the Panasonic GH1. It seems the camera has a blue channel banding issue. I hope Panasonic can fix it soon.
UPDATE: It seems the same effect is present in the red channel.
UPDATE2: You can download a video sample from the GH1 from here: http://www.dvxuser.com/barry/PRIVATE.zip.
You can read the forum post at dvxuser.com.
UPDATE3: More videos for dowload avaiable here: