Just had to try it, I received the Nikon -> M4/3 adaptor yesterday, and attached it to the G1 today with the Tamron 90mm Macro. Took a few quick shots in our garden in late afternoon light, all hand held at very slow shutter for the most part, and Aperture at f8 or f11.
Shooting with a 90mm which = 180mm hand held is a bit tricky, but I got a few good shots, the bokeh on this lens is excellent. Will try some with a tripod as well.
Shot in RAW but really I do not see much difference in the camera JPG vs the RAW, but of course easier to adjust.
A pink Begonia flower, was in shadow so used the onboard flash.
Flame Tree close up
Stag Horn fern