My 90mm f/2.5 Summarit-M lens was returned from Leica yesterday after being repaired. The aperture ring had worked loose and they had fixed it under the passport warranty scheme. It was a quick repair for Leica. Only a few weeks and that included the Christmas and New Year break.
I checked it out with some indoors shots of a few camera lens combinations (camera porn!!) and in a brief burst of sun a few outdoor shots.
The camera pictures were taken at f/16, which is the minimum aperture. Unlike other lenses, the minimum aperture on this lens is extraordinarily sharp. For distance shots at wide apertures, the rangefinder focusing is quite difficult, which is a problem I find with telephoto lenses on the Leica. I had an excellent old 135mm f/4 lens, but sold it as I was getting a lot of mis-focusing. The focusing area on the rangefinder is very small, and while subjects near the camera are fine, the further away they are the more difficult it is.
There's a couple of interesting articles on the differences between SLR's and Rangefinders in the following links:-
http://www.photozone.de/slr-vs-rangefinder - from Photozone
http://www.kenrockwell.com/tech/rangefinder-vs-slr.htm - from Ken Rockwell