After a conference or happy hour, many people find their pockets stuffed with business cards. If it was a productive event, the next morning you may be unable to pair each card with a face.
For the faces you remember, it's customary to send off a nice-to-meet-you-hope-to-see-you-again e-mail. Often, the reply is just as trite.
This is the 1.0 way to follow-up: toilsome and monotonous. First you need to remember what you discussed, then you need to ...