I have a pretty good idea why -
The CCK works well if you don't try to import a lot of images. If I use the SDCard out of my D90 with ~50 photos, the import goes smoothly. If I try it with more than that, though, the Photos app crashes. This happens every time.
I've had the CCK since I received my iPad 3G in late May (my pre-order showed up one day before the release day in France).