5D with Leica R lenses?
....slightly off subject, but thought this might be of interest:-
I've been using a cheap ebay 'special' adapter to mount old Olympus Zuiko lenses (& accessories) onto my 5dmk2.
Check out http://www.16-9.net if you have not already - some old zuiko's are actually very good optically (& alot cheaper than comparable lenses).
I think using manual lenses on Eos system is most appropriate at the wider end of the scale - I have an OM 180mm f2.8, but I'd much rather use the 70-200L f2.8 IS for the IS & AF features - & Canon's tele's seem to be pretty good (at least relative to their wide angles I think). My subject matter with tele's benefits from IS & AF more, while my subject matter with wide angles tends to be more static & therefore I don't miss IS & AF anywhere near so much. The Om Zuiko 24mm is meant to be relatively good optically, as is the 18mm.
I have found manual focus is okay with 'normal' lenses.
However, I have also mounted Olympus extension tubes & bellows unit & macro lenses onto the 5dmk2 (I had to use an extension tube between the bellows unit & the 5dmk2 as the bellows unit mount surround clashes with the top of the 5dmk2 & you can't mount directly.....its not a probalem at all having to use one of the extension tubes though). With one of my more extreme combos the viewfinder is VERY dark as the lens does not automatically stop down & at the extreme magnifications I can achieve I need to stop down to get abit of DoF to work with. The particular lens in question is an OM 20mm macro lens (f3.5 I think) but it has an RMS mount & has to be used with an RMS-OM adapter itself - its basically a microscope lens (that is what the RMS mount system is) but with this setup I can get the 'E' of Elizabeth on a £1 coin to cover full frame - to give some idea of magification - its an area about 1.5mm x 2mm. I have never done any macro work before - I now have a healthy respect for those that do!!!