I've got the G3 and really am impressed with it. I stopped carrying my DSLR when hiking years ago and began using compact p&ss, including the great little Canon S90, but the image quality of even the best compacts are fine for emails and posting on-line, but don't meet my semi-pro standards as images can't be printed larger than about 8x10, can't really be cropped, and can't be used for print publication except in a real pinch. I believe that the m4/3 sensor is more than 4 times larger than the high-end compact p&s sensors and it clearly shows.
I bought a G3 in Sept. and have taken it backpacking on 3 5-day hikes this fall. Its amazing to have a camera with three lenses--Oly 9-18 wide zoom, 20 1.7 low light prime, and 45-175 x tele zoom--that I can take up the mountains. I also have the 100-300 and kit 14-42. The 100-300 is too heavy for backpacking, which is why I got the new 45-175.
The G3 only weighs 2 oz more than the gf3 and has evf and articulating screen, which I use much more than I thought I would. It shoots great video, though not with as much control as the GH2 and it doesn't allow you to use an external mic, like the GH2.
Image quality is very good and with the fast primes, low-light photography approaches excellence. That said, the image quality is not as good as my Canon 50D and 600D when printed larger than 13x19, but up to that point, it is hard to see any difference. My biggest complaint, as a fairly serious wildlife photographer, is that there are no prime teles that compare to the Canon 300 f4 IS. The 100-300 is nice, but other than the 70-200 f4 L, I've never met a tele zoom that had the quality of a tele prime even with other Canon L lenses. And the 100-300 is not an L in resolution or color rendition--then again, its 1/3 the price of any tele L. And supposedly we will see Panasonic release a 35-100 high-end lens this winter.