I hope you do not rush into buying Olympus cameras too soon.
E520 510 or 500 (Same as E420, 410) use pretty much the same sensor. They all suffer vertical banding problems when the image is underexposed by 1 1/2 stop. The cameras work well when the scenery you are photographying of similar light intensity. Too much highlight and shadows existing in one image is usually a disaster regardless what lenses you use.
E3 performs better in terms of noise issue. It has beter ISO telorance up to 800 or so. Its autofocus is better comparing to the rest of available bodies. Even the latest release E30, the autofocus is not better than E3. E520 autofocus is not as good as E3 by a huge margin. I think you would need to know this.
Speaking of G1, the adaptors are going to be 175 US dollars. I would wait until the camera pricing comes down. After all, I had been waiting for G1 for some time to test out my voigtlander leica mount lenses.
Do not rush into decisions. I test these things out because there is a huge olympus photography group here in Melbourne and I happen to be part of the group.