Adding a Bump-like feature to Facebook would be a good idea, you're right. My main problem is the physical act of bumping the phones together. I cannot picture ever being in a situation where I'm going to share info with someone (contact, photo, movie, whatever) and then one of us has to go, "Ok ready? Go." and we tap our phones together. So awkward.
If NFC was involved, you could each load the Facebook app, and then tap on "share" or something. A list of people in your immediate area that are also running the software in "Share" mode would pop up, and you'd tap the names of the people you want to share with, and the info would be pushed wirelessly to them.