My own justification for owning and using an M8 is that I like doing so, and the files it produces suit my requirements and are quick to adjust for how I want them to be. Add to this the size, weight and familiarity and I'm more than happy to use one. Although the web would have you believe that reliability is a huge issue, I'm cynical about the web's ability to differentiate between a small or a big problem as opposed to a vociferously announced one!
I certainly think that liking a camera is a good reason for shooting it, and I do that myself -- and I also shoot Nikons because I like them better than Canons, not because I think they make better photos.
I'm also somewhat cynical about web judgments, but not when it concerns the Leica M8. I read the main Leica forum, and virtually everybody on the forum, it seems, has had a very serious problem with their M8-- these are not people who are self-selected *because* they had a problem, but Leica enthusiasts who were anxious for the M8 to succeed, and then had serious problems.
The first batch of cameras actually had a mechanical/electrical problem that had to be fixed. I sent my camera back to Solms, and it was fixed. That took two months. Then it broke again, a month later, and this time, after examining it, Leica gave me a new camera. The M8s failed so often, and so comprehensively, that certain problems were given specific names, and when you developed those specific symptoms, you knew you were toast. If somebody put a gun to my head and demanded that I produce a percentage number of failure-in-use of the M8s produced before, say, last February (that is, from the first sales in November of 2006 through February of 2007) I would say that number would be greater than 60 percent. That does not include cameras that had to be sent back for the mandatory repair (which would push the number to 100%), but didn't actually fail in use.
One of the members of the Leica forum, am engineer, actually disassembled an M8 and the M8 battery charger. The assembly quality of the charger was disgraceful. It looked like the inside of a $2 flashlight.
I carry my M8 all the time, for the reason you gave above -- I like it. But it has lots of problems.
Rob -- I don't think we disagree. However, the M8 gives the IQ equivalent of a top-line DSLR, IMHO. If Nikon produced a body the size of an F3 with the D3 chip inside of it, and with (only) M8 battery life, I would buy it in a minute (and use Zeiss primes on it.) Unfortunately, the top-end Nikon/Canon cameras weigh more than some LF cameras, and also have a huge, obtrusive frontal area; and as I pointed out in another post, some of the common lenses (like the Nikon 17-35 zoom) are, by themselves, as large as the Leica camera. *That's* the problem with using DSLRs in candid photography; it's not the IQ.
If you're doing some heavy duty PJ or studio work or whatever, and failure is not an option, you put up with the size and weight; it's the job. If you're going out for a ramble in the woods with the dog, or down to the art fair, the Leica's nice.