Owned an R8 and loved the ergos. Absolute joy to use. Thought about moving to DMR and used one from friend. Great IQ, etc. That said, it is $5000+ for a cropped 35mm with AWB that can be a bit 'odd' at times.
Instead opted for Leica glass on a 5D and now 1Ds2. The lenses from Leica are second to none and REALLY make the Canon sensors come to life like EF glass just can't. Have owned, own or tested the 28/2.8 V2 (now for sale), 50/2, 60/2.8 M, 80/1.4, 90/2, 90/2 APO, 100/2.8M, 180/3.4 APO, 180/2.8 APO, 180/2 APO, 35/2 and probably couple others. Faves were/are the 28/2.8 V2, 35/2, 80 'Lux and 180/2.8 APO.
Ok, now that the praise is out of the way, there are some drawbacks to going Leica R. You're paying a BIG premium, even used, for an extra Nth % in performance over Zeiss or even some MF lenses via an SLR adapter. The lenses are also slow to sell second hand if you decide you want to shift around your glass. Small market.
Service turnaround from Leica (if the gear has to go to Solms) can be horrendous - can sometimes be measured in months, even for a simple CLA. They are a small almost bespoke shop and they do things on their schedule, not yours.
Also, IF an R10 as people hope/expect it to be (pro-level integrated grip FF DSLR sans AA filter) doesn't materialize at Photokina, prices on used R glass will drop significantly as it will signify an effective end to the Leica R glass line (when was the last time Leica introduced a new R lens?).
There is also some concern, as much as it makes no business sense, that any new R10, IF it appears (and there is a LOT of doubt about that) may be AF and if so, MAY not be compatible or easily compatible (trip to Solms or adapter) with legacy glass. Again, makes no sense from a business perspective, but we're talking Leica here ;>
More seriously, Leica execs when asked this question in any number of interviews have refused to even confirm that older glass will be mountable on any new body - IF it comes to fruition.
There is no question that the Leica gear delivers the goods, but you need to go in with your eyes wide open. If I had an unlimited budget and multiple top-quality bodies as backups , I'd buy a DMR. Sadly that budget doens't exist.
On the glass side, the IQ is there in spades; IQ that can be milked further using the AA filter-less DMR. That said, I'd look at testing some R glass first on a top Canon body as part of my eval process.
I tested a DMR against my 1Ds2 using the same R lens and the shots were indistinguishable, which says a lot for the DMR, but also means there are less expensive body options out there with which to use that lovely glass.