In my experience Leica digitalis are the most temperamental and high maintenance cameras I've ever owned. Of course, a rangefinder is different to a DSLR, so it comes with its own unique issues (for example, misaligned rangefinder mechanisms) that I can accept.
But, there are lots of other issues that should not be there, such as the camera locking up; hot pixels on the sensor (yes, I know about the cosmic fairy dust arguments, but I've never experienced this issue on any other digital cameras that I've owned) and SD card issues.
Both of my M8s had hot pixels, with the first one requiring a remap; it also had the coffee stain issue. Both have locked up occasionally. One segment of the viewfinder LED no longer illuminates on my M8.2.
My Brand new M9P arrived with hot pixels on the sensor!
These problems coupled with the hassle and cost of getting them repaired make Leica digital ownership a real labour of love. Any potential owner should be alive to these issues before committing his or her money, and as one person has said, be prepared to write off the M8 should problems develop because repairs won't be cheap.
That's not to say digital Leicas are duds. They are a joy to use and deliver brilliant images, but when your camera is faced with yet another trip to the shop or locks up just as you press the shutter, it can seriously piss you off. So, by all means buy a secondhand M8, but hope for the best and expect/ prepare for the worst!
Would I buy another one? Yes I would, but it would have to be an M8.2 and cheap, I.e. less than £900.