It's been awhile since I've uploaded a pic with metadata to facebook, but I faintly remember that Headline, Description(/Caption-abstract?) and a copyright tag were imported. But it's easy enough to test. Upload a photo with a lot of metadata filled out and set it to private.
Since I have such a test photo, I tried it out. Each tag in my test file is filled with the name of the tag. The result was that it copied IPTC:Headline, a blank line, and then IPTC:Caption-Abstract into the Facebook description field. Also, even though there was GPS data and timestamp, it didn't copy either from the file. No copyright tag was imported.
