In reply to malk:
There's not much difference in size between APS-C and m4/3 so I wouldn't choose a camera based on that difference. There's no big advantage to either one. The slightly more square format of m43 allows slightly smaller lenses.
If one of those isn't large enough then really the choice is between those and full frame. Full frame is good for low light, blowing up images to a very large size and a shallow depth of field. This is offset by the size and price of lenses, plus the fact sometimes a longer DOF is desirable. Probably depends to some degree on what you're shooting. Some professionals are now using m4/3, so for general use the image quality is very good.
The analogy with betamax isn't that good since with an lens adapter you can use any lens on m4/3 (though the AF may not work). I think the lens selection is increasing all the time and m4/3 cameras are very popular. With both Olympus and Panasonic behind them I don't think they'll go away any time soon.