I'm firmly in the 4/3 camp having switched from Canon to Olympus years ago. The smaller sensor only matters at very low f-stops when trying for selective focus. The mirrorless cameras will probably supersede the SLR's as the line between still photography and video blurs. I use both micro 4/3 and the original 4/3 cameras. The sensor size is the same, but the micro 4/3 cameras and lenses are smaller. A 35 - 100mm, f 2.8 lens would replace my old 70 - 210mm, f 2.8 35mm format monster. That was probably my all time favorite lens, but it was huge.