rather the desktop version seeing the tags/ratings from the photostream.
I'll look there as well though,
"My Photo Stream" is populated automatically from photos taken on your iPad. It will show the photos exactly like they have been taken and not sync with any edits applied to them later.
So the PhotoStream will always show the original version. I have not tried to share the edited version from the Camera Roll to a shred photo stream (using the Photos.app), but that should share a version with the edits applied.
To get your captions and keywords from the iPad to the Mac, save the edited versions back to the Camera Roll - you can do that in iPhoto on your iPad from the Share menu. When you dowload the camera roll photos from your iPad to the mac (connect it to and USB port) and import to iPhoto, the keywords and edits will be visible (in Aperture I even see the caption, but not in iPhoto).
-- Léonie