By far, the Panasonic GF1 and Olympus PEN are the dominating the micro fourthirds market. They are way ahead the competition, simply because many of the major brands have not yet entered the micro fourthirds arena.
This morning I read an article about the upcoming SonyAlpha NEX on sonyalpharumors.com and wired.com. Still no announcements of Nikon or Canon entering the market. Wired calls them “EVIL” (Electronic Viewfinder Interchangeable Lens) cameras. I would prefer an optical viewfinder, or at least a high-quality built-in electronic viewfinder, not an accessory that you put on top of the camera.