Good news to report on Leica R lenses.
I bought a couple of R lenses for my A7R, mainly because they are cheap as chips compared to M lenses, whilst still apparently being of very high quality. I got a Summicron 2/50 and an Elmarit 2.8/90.
Disadvantages - they are larger than M lenses and the adapter is thicker, making the camera & lens package larger. Long focus throw compared to M lenses.
Advantages - beautifully made, lovely clicky aperture rings, buttery focus, slidey out hoods. Image quality seems top notch.
Having never used a Leica R lens before, I'm very impressed. These two cost me a total of £550 inc a 12 month guarantee from Aperture in London. I had a wander out today, and the results are in this set on Flickr. I've tried to put aperture info in there as accurately as I could. Pics are unprocessed out of camera jpegs aside from some small exposure tweaks in Lightroom to avoid personal embarassment

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http://www.flickr.com/photos/tobinators/sets/72157637943103785/

A7R with Leica Summicron-R 2/50 by
Tobers, on Flickr

A7R with Leica Summicron-R 2/50 by
Tobers, on Flickr

A7R with Leica Summicron-R 2/50 by
Tobers, on Flickr