Nikon has just announced their new lineup of mirrorless cameras, the J1 and the V1. The J1 and the higher end V1 come with an all-new 1" sensor, with a 2.7x crop factor. The new sensor format is called CX, and the new lens mount is called CX mount. This new sensor is significantly smaller than the Micro Four-Thirds and the APS-C sensors (shucks).
I think Nikon is taking a very big risk. It could trigger a backlash from Nikon loyalists, at a time when Nikon is already facing a declining market share. I think Nikon should have stuck to the DX format. Since the F-mount lenses can also fit into the DX-mount, many people would have happily bought into a mirrorless camera based on DX sensor and mount. By starting a totally incompatible line of CX-mounts, Nikon will be splintering its own customer base. Many Nikon DSLR owners will have no reason now to maintain undivided loyalty to Nikon. When purchasing a small body DLSR system many will now start to look at Sony, Panasonic, or Olympus. Unless the new CX sensor is able to provide unprecedented image quality (very unlikely) and is proprietary to Nikon. Good luck, Nikon. All eyes should now be turning to Canon to see what they are going to do for a mirrorless camera. And I hope they will have the sense to stay with APS-C.