Here is a first attempt at comparing lens performance on the G1. Weather was rotten here today with sleet and rain so I just took some shots out my back door. This shoot compares the Panny 14-45 kit lens to the Oly 12-60 SWD, both at about 45mm for this first shot that I posted. Details on the pbase comparison page. Looks pretty much like a wash to me so far - no dramatic differences. Other shots at 14mm and 25mm led to the same conclusion. I used the Panasonic 4/3 to m4/3 adapter for the 12-60 and manually focused both shots with maximum magnification on the LCD, tripod mounted.
I'll do some more when light is better outside.
PS - I used a custom made profile for the G1 with the DNG editor and a shot of the ColorChecker Chart for use in LR, but not that much different from the standard LR G1 profile.