This is a series you must see. Lasse Eisele shared an impressive series of landscapes shot with the Lumix DMC-G3 (and Olympus lenses) in Swedish Lapland. The images are just gorgeous.
(Click Here) to see all of the images on dpreview.com.
Lasse expresses general overall satisfaction with the G3, yet comments on weak dynamic range and clumsiness of the design of the camera controls. I can add that the G3 indeed does do better in low contrast situations, if you're looking for tonal range. Of course, that's true of any film or sensor, but it is an area for improvement in the G3 sensor.
Related to accidentally hitting controls that you don't want to hit, I feel the pain. I have more than one accidental video, for example, which causes a several second delay in getting back to still photographs. You can turn the button off in the menu, but then you can't respond quickly when you do want to shoot a video.
I imagine the GH3 may improve performance in both dynamic range and control layout. However, that comes at significantly higher cost and large overall size than the G3. It all comes down to compromises. The G3 is a pretty good set of compromises, overall.