Kashmir Hill observes:

Nowadays, if you’re not on Facebook, it’s possible you don’t actually exist. There was a time when we had to exchange phone numbers or email addresses to keep in touch with a new acquaintance. Now, we usually just head to Facebook and friend them.

The same holds true for business cards, which presumably have declined in use because of Facebook's omnipresent reach.  After my initial infatuation with the site, mostly as a means to track down far-flung people from the past, now I just use it as a directory.  So it has largely replaced the phone book as well. I met someone in New York last week and it simply didn't even occur to me exchange information. (And now, to friend someone, you can simply shake your iPhone.)