I handled the new 100D at the store today. It was a display unit, but I didn't take any test shots as I just wanted to hold it and see how it fits.
It really feels nice especially if you mount it with a small prime (so, anything with a red ring is out), the grip is still holdable though suffers from the same problem as the Rebels -- the last pinky finger usually has nothing to grip on. I can't imagine anyone wanting to get an EOS-M after handling this little thing, if only Canon produced a matching EF-s 22mm f/2 lens for it.
But anyways I am going to give this a pass. Besides the 35/2, I don't have anything I would want to mount on this camera and have it still balance properly in my hand.