It has been a couple of months now since I've switched entirely to Micro Four-Thirds with the OM-D EM-1. I cannot say that I am disappointed in any way. It's solid, light and has amazing image quality for the sensor size. I'd say that the quality is indistinguishable to me from my work with the D700. I have never used a D800, and I am quite sure the quality on that camera is mind-blowing but I've never had the need for 36-MPix - not up to the sizes I print anyway, and the advantages in size, versatility and silent operation are certainly not to be ignored.
As some of you will know, my recent work has mostly centred around nature abstracts, and I have found some great advantages in the EM-1 that were hard to come by with the DSLRs. First off the live bulb function allows me to compose my images more accurately during long exposures, particularly at night with multi-second exposures. The ability to use the screen for this also allows me for more freedom of movement which makes the work even more daring, if I may use that word. I have already seen some evolution in my style using the OM-D, and I hope this will continue as I become more acquainted with this little gem.