I'd re-iterate what Jack says. The 28D is good but not right to the corners (I suspect some are better than others) and my Schneider 35XL is very good even with shift. However it may be that the problems you've heard about are less to do with sharpness and more to do with lightness falloff and there are indeed problems here. If you use a centre filter (and you'll lose a stop or two if you do, which means that on anything but a very bright day you will always need a pretty reliable tripod setup) this problem goes away but if you don't, electing instead to re-balance the brightness across the frame using software, you will in effect be exposure compensating the corners upwards by up to a couple of stops and this will mean risking quite noticeable noise increases in some scenes, depending on what is in the corners (shadowy areas in particular will start to look a bit grungy) and this will likely be worse if you use Zero Latency rather than a wakeup cable, depending on ambient temperature and the length of time you leave to back 'on' for.
The other issue is colour shift and the need, on technical and field cameras to make LCC shots through an opaque panel. The Dalsa sensor is less prone to colour shifts than the Kodak sensors, but the problem is still there and it still needs dealing with and when you do apply the LCC shot you've made, you may want to choose the option not to correct light falloff or only to apply it partially or you may run into the noisy corner issue.
However, in my experience with the system so far, these issues can be worked around with experience and good technique and are in no way to be seen as a deterrent!
Best
Tim