when i decided on an inexpensive way into digital rf shooting i chose the epson rd1 over the m8 for the following reasons:
huge 1:1 viewfinder vs .68 (one simply cannot overestimate how valuable this is in practice, as it allows shooting with both eyes open and provides the eye with exactly the view it would get not using a vf);
user-choosable individual framelines in VF vs camera-chosen cluttered 2 sets;
no need to fool with IR filters on lenses;
virtually no focus shift or color cast on any M lens vs problems with many UWA and some WA;
no need to 'code' lenses;
useable lovely results up to iso1600 vs cant shoot above the wierd iso640;
fold-into-camera lcd vs standard non moveable lcd;
ability for user to (pretty) easily align focus patch vs having to send m8 into the blackhole of leica service.
the sole 'deficiency' of the epson vs m8 is 6mp vs 10mp, but if anyone can tell the difference in side by side they have my undying admiration. i certainly couldnt, and even if i had, the ability to shoot at 1600 would more than make up for it.