I've not put the camera through a lot of paces yet, but I wanted to quickly evaluate image sharpness with my copy. Shooting around the house with my Nikon 85/1.4 left me smiling. I also wanted to see if my Sigma 150/2.8 macro would focus normally. Again, no problems.
Here's an example with the Sigma 150mm along with a 100% crop. I think the new sensor has plenty of resolution. Shot on tripod using Mup and remote shutter, ISO100, f/4, 2sec exposure. I processed these with LR3.3 Release Candidate.