;alkdfad;lfk - Does Image Capture app work? or iPhoto? - Nikon images captured straight off camera not showing thumbnails is a preexisting problem, so that isn't new to DCRCU 2.3, though capturing from a card reader hasn't been a problem before
Unfortunately it hasn't fixed the issue with some Nikon D2X NEF files displaying the "Unsupported Image Format" message. It's better than it was - previously about a third of my older files wouldn't work, now I'm down to perhaps one in twenty - but the problem is still there.
When both the RAW and JPEG are download into Aperture, the only evidence you ever see of the JPEG is by control-clicking on an image and see if New Version from JPEG Master is offered. If it is, the JPEG is there as an otherwise hidden master.