any clues, weight vs image quality vs longevity?
I recently bought a E-M5 and from my past experiences with the 7D, I'd say the image quality is similar, although I want to add that the dynamic range of the OM-D is quite incredible. I bought it as a companion to my 5D series cameras and I now take out the OM-D a good deal of the time over my bulky, conspicuous digital SLRs.
The OM-D obviously wins in terms of compactness and weight.
The Olympus's one-shot AF is also quite remarkable -- and from my own observations sometimes more reliable than the 5D Mark III's in low-light.
If you're not a professional or/and highly prize compactness, I'd say the OM-D route will serve you well. The 7D is still -- despite is "age" -- a highly competent and versatile camera and far from obselete.