I've got a G1. I had a GH2. I've ordered an OM-D. I owned a Nikon D7000 for a couple weeks. I've owned 7 other Olympus DSLRs. I used to have a D300, and I owned a D40. I also owned K10D and K20D Pentax's. What I've found is that the sensitivity, the true ISO delivery of each sensor was different. Noticeably so. The Pentax sensors were about 0.7 stops slower at a given ISO than the Olympus cameras. The GH2 is at least 1/2 a stop slower than my G1 is. The OM-D is apparently even less sensitive. You can equalize illumination levels easily enough in post-processing, but reported noise figures and example images on websites mean little if the exposures and apertures used are different. An expensive f2.8 lens becomes (in effect) a much cheaper f4.0 lens on a camera with a less sensitive sensor. I can't understand why something with such an impact isn't being talked about more.