The Olympus is a wonderful camera. Many people have moved from full frame and APS DSLRs due to size and weight issues and have been very happy. It's a much better camera than the Nikon V1 based on everything I've read.
It's much smaller than a D600, but can do just about everything well other than very shallow depth of field and tracking AF. Image quality is top notch. Even some D800 shooters own one as a travel camera.
You can buy a new OM-D with the 12-50 for $1200.
A great source of information is the dpreview micro four thirds forum.
http://forums.dpreview.com/forums/1041There are many threads comparing the OM-D to DSLRs.