Many professionals have started to use the M4/3 system, and that's even before the rather more capable and solid OM-D model hit the market. I think the system has a very interesting future for enthusiasts. Scratch that, already the present is very interesting, the future possibilities blows my likkle fragile maaahnd.
Below is a comparison which may actually come closer in terms of quality and capabilities, the Canon 60D and the OM-D. Look at that size difference! And the D60 is not a large camera for a mid-level DSLR.
... And if you go with the lens-compatible Olympus Pen Lite (about the same image quality, but less features and ruggedness), well...
Of course most of these gains are of course due to technological progress, which other makes may be able to replicate. But oddly and sadly none of the big makers (Canon, Nikon, Pentax) have so far shown much interest in the compact interchangeable-lens market, apart from a couple of efforts (Pentax Q and Nikon 1) which have sensors so small that serious photographers have trouble taking them, well, seriously. And for any of the big boys to join the M4/3 system is probably well too strongly against the corporate male-ego principles! It would be like Mercedes and BMW making compatible spare parts, oh the disgrace!
Thanks to Bruce who pointed out where to find the well-hidden feature of adding lenses... (tiny link at the bottom.)
OM-D and 60D with Normal lenses (roughly, 20mm 1.7 (40mm equivalent), and 50mm 1.8):
I like that the OM-D is only 400 grams, body-only. Not feather-weight, but still about half the weight of a middle-class DSLR.