Although it seems nice to have smaller and lighter, some of those of us, particularly those with large hands, find it easier to hold full frame cameras. Myself, I find that the point-and-shoots are too small to hold properly and as a result, when I press the shutter, the camera moves. Not a problem with "real sized" Canons, Nikons, and even the Olympus 4/3 cameras.... but micro 4/3 cameras and point/shoots and PARTICULARLY I-phones can not be held steady in my hands.... the same hands that can track the space station through an 800mm lens!
I love the promise of mirrorless but until they arrive at a balanced body that I can hold properly, I'll stick to my DSLR's.