[adan]

When the M8 was touring Denver two weeks ago, the Leica reps would not let anyone put a collapsible lens on the body. Even the 90 macro - unless it had the macro extension mounted. Not even the current 50 f/2.8.

They said that Leica would specifically recommend AGAINST using collapsible lenses at all on the M8 (except the macro with the adapter) once the final user's manual is available, and that the existence of collapsible lenses is one of the prime reasons that the M8 does not come with Passport protection - Leica will not cover damage to the shutter/sensor from collapsed lenses.

"given that the M8 ...must have the same back focus as other M's, it follows that the shutter blades will be at approximately the same position as the cloth of the conventional M-shutter."

Not at all - the shutter could be 1mm in front of the sensor or 5mm in front of the sensor. Some early SLRs used their mirror as the shutter. You are right that the lens-to-sensor distance must be the same as the lens-to-film distance in film Ms - but the shutter CAN be anywhere in the 28mm of space between the lens mount and sensor/film. In the M8 the shutter is reasonably close to where it is in film cameras - but it only take a couple of mms to foul on a collapsed lens.

Also, metal-blade shutters are thicker than a cloth/rubber shutter curtain.