There are two official and one "unofficial" M8 bodies... The official ones are the M8 and M8.2. In between is what some like to call the M8u - just to distinguish it. You know how it is with Leica stuff and names...
Basically, the M8u is an upgraded M8 with one or more features from the M8.2. The big ones are:
- Updated framelines (more accurate, tuned from .7m to 2m)
- Upgraded shutter (no 1/8000s, quieter)
- Sapphire LCD cover glass
There are other differences between the M8 and M8.2 that weren't available as options. Things like the black dot, new skin, etc.