Yes indeed - and I guess that the Ricoh has done something so that wide angles work well?
I spent three days doing a bunch of real-world captures with the CV Skopar 21mm f/4 lens on the GXR+A12-M, examined them thoroughly last evening. I see no corner-edge smearing ... clean resolution all the way to the corners.
Shooting a scene with a peripheral flat white wall netted what looked like some color shifting (see the Ricoh GXR threads, can't remember which one, for the "Too Many Bears" photos), but the main illumination in that case was the television and it doesn't pose a satisfactory test due to all the weird lighting from that and the sunlight from the windows. I'll have to rig up a more rigorous test.
BTW: These are all raw captures processed in Lightroom, so whatever in-camera image processing to correct issues might do I can't say ... I haven't even looked at that yet, but I believe it works only on the in-camera JPEG outputs.
I've tried the GXR+A12-M with several lenses now: the Skopar 21mm, the Skopar 35mm, and the Nokton 40mm all seem to work very nicely with it. I fitted a mount adapter and took a couple of exposures with Nikkor 85/1.8 and Micro-Nikkor 55/3.5 lenses ... they also performed very nicely. Today I'm fitting the Skopar 50mm f/2.5 for some testing, after which I'll test the M-Rokkor 90/4 and Ultron 28/2.
Overall, whatever Ricoh has done in the technology, I think they've done an excellent job. I hope (and expect!) Leica to do even better.