This is a Nikon forum. You'll be better off asking about the X100 versus M8 in a Fuji or Leica forum. However there is already an X100 and what that means for Nikon discussion going on. You can read some opinions about the X100 there. The X100 is not a rangefinder. I wouldn't compare it to a true rangefinder like the M8. That's a totally different camera. I also wouldn't say spending $2000 more for an M8 is just, "a little more" then buying a X100.

Currently at Amazon you can find a Leica M8 refurbished for $ 2700, of course there will be another at least $ 3000, for a lens. But then you will have no uncertainty that the camera will perform to your professional standards.
Obviously, neither camera is for the average people, but all this fuzz about the Fuji X100 does not help much to understand the pros. At this point it s kind of a gamble to buy one, but if it finds a niche among photographers, there won't be any available for a while...