I have a d2X with V2 firmware and the serial number does show up in Adobe Bridge. Indicates its not a bug on a d2x.
Marty,
OK - I think I know what is happening. It appears that Nikon doesn't write the serial number for JPEG photos, but does for NEF RAW files, and this may be the change in v2.00 firmware for D2X (but not D2Xs or D200). The reason for this may have something to do with the encrypted white balance (according to ExifTool, the serial number is part of the key needed to decrypt the white balance, and you would only need this for RAW files presumably).
The jury is still out on this one until I can get some more files to look at. In any case, if PM 4.4.3.3 doesn't show the serial number, then it is probably not there since as far as I know we are looking in the right spot in the maker note for the info. If you are viewing RAW+JPEG pairs, you will need to split these (View menu in PM) in order to really tell whether or not the photo has the serial number, since PM will be showing you the JPEG info for a RAW+JPEG pair.
If anyone knows whether or not Capture or Capture NX shows the serial number that would be nice to know.
--dennis