GAS = Gear Acquisition Syndrome.
I love my Rangefinders, and I love digital.
The discipline inherent to shooting RFs is very different. There is definitely an aspect of it that is somewhat anachronistic. Think of it a little like adding complexity to something that needs refreshing - like telemark skiing, for instance.
Rangefinders take you back to a more classic way of shooting - all manual, with primes - that actually makes life a little easier once you're back in the groove. I find I ultimately spend less time thinking about the mechanical aspects, and more about composition and the image per se. Both the R-D1 and the M8 have an Aperture Priority mode, and then all you need worry about is focus. And if you're shooting in the street at f/8, everything more than 5 feet away will be in focus anyway, so all you do it bring up the camera, take your picture, and move on.
Also, because you can't just "fire away" with an RF, I find that I come home with a lot less shots... but a lot more keepers.
It's really quite simple: if you want to shoot people, a high-end SLR with a fancy lens is like pointing a gun at a person. A small Rangefinder looks to many people like a Point-and-Shoot. You can go places and shoot things you'd never have access to with a big SLR, no matter how self-confident you are.
There's also a question of equipment fetishism - at least in my case. For instance, the R-D1 has a manul lever for cocking the shutter after each shot. I absolutely LOVE that.