Very interesting. As is often the case, it can come back to what an individual shoots, as well as how. There is no doubt in my mind that some of the strengths of other sensors can become apparent in some shots, and of course if there are many small differences, they can cumulatively make a real difference in some circumstances. For example, there are some photographs made in a session where I have used several cameras that I can identify clearly as coming from my full-fram Canon. Many (most) times though, I cannot.This is true for photos taken in the ideal circumstances. When I use controlled studio lighting, my Panasonic G2 almost always produces wonderful results, as does my Samsung EX1. Even my cellphone takes wonderful pictures in the studio
However, in real-world situations there are many factors that make Micro 4/3 perform significantly worse. The problem No. 1 for me is G2's relatively narrow dynamic range, especially when coupled with its live view histogram which is far from truth. And don't even get me started on Micro 4/3's perennial difficulties with brightly-colored objects (yellow, orange, red, violet etc.) which inevitably lead to single-channel clipping and all kinds of weird color shifts. There was a thread on Mu-43.com dedicated to exactly this issue and it was pretty clear from the image samples in this thread that even GH2 in that respect is closer to small-sensor compact cameras than to APS-C DSLRs and CSCs. For example, I incidentally discovered that there are whole families of flowers whose colors can not be reproduced with reasonable accuracy by any 12 MP M4/3 camera (for example, most species in the genus viola). I found it out when a friend of mine asked me to shoot her prized flowers — I was forced to rent a Canon DSLR to finish this relatively simple task.
Do you know anyone who has one of the contenders for your new camera? If so, can you borrow it for a day or two? I suggest that you do a real-world shoot-out, using RAW images from the borrowed camera and the G2. Shoot the things you normally do, and of course some of the things where you have experienced challenges. Of course you will pixel-peep the images - but then process them to your preferred output. Look for real differences that are meaningful to you in the finished product.