I finally got a hand on a Panny G1 in Houston. Out of all places in the world, Microcenter was carrying a G1. It's currently "on sale" for $630.
I can't comment on image quality given that I don't own the G1 and did not bring a SD card with me. But I played with the G1 for about 20 minutes in the store, and was very impressed with the ergonomics, build quality, and the usability. The G1 is small, very small. Definitely smaller than my E410. Yet, it's easier to hold thanks to the pistol grip. The buttons are well placed, and the controls are very intuitive.
I loved the electronic viewfinder. It is like watching a TV, but a nice and bright TV. It is FAR FAR superior to the tiny optical viewfinder on the E410 and 510. The image looks huge and bright throught the EVF. I've read that the EVF has trouble tracking fast moving objects and it looks horrible in low light situations. I can't comment on that, because the area was well lit. What I can say is that after getting home, I looked through the viewfinder of my E510, and I felt like I was making a trip back in time to the 1900s.
One of the cool features about the EVF is how the EVF automatically zooms in when the G1 is in manual focus mode. So while it's nearly impossible to manual focus through the optical viewfinder in the E410 and 510, it's a piece of cake on the G1.
I had my fears that the G1's full time constrast based AF would be slow like the constrast based AF in the E420/520/620/30. And that it would definitely be slower than the phase shift AF while using the optical viewfinder in other DSLRs. My fears were unfounded. The G1's contrast based AF actually found focus fast! Very fast! Of course I did have good lighting inside the store, so it might not focus so fast in bad lighting. But while in the store, the camera's AF was very snappy.
After being disappointed with the E620, I am tempted to get a G1. The limited lens lineup is a bummer though. I do have the Oly 14-42, 40-150 and 25 pancake. So all of those would work with the G1's AF. But the G1 does not have built-in-body IS.
If there is someone wondering whether to upgrade from a compact to an entry level DSLR, don't forget to look at the G1.
E620 | 25/2.8 | 50/2 | 12-60 | 14-42 | 14-54 | 40-150 | 70-300
Olympus E-P2 | Panasonic GH2 | 20/1.7 | 14-42 | 14-140
Leica M7 | M9 | 21/4 | 35/1.4 | 50/2.5 | 50/1.5 | 70/2.5 | 90/2
Sony NEX-3 | 16/2.8| 18-55