Ever said, “I met tons of people at the bar/tradeshow/etc. conference, and got a load of business cards, but nothing ever comes of it in terms of business development.” It may have something to do with your erroneous belief that things will just happen – i.e., enough of those you met will remember you and what you do; and either they will call you about a legal matter or refer a client to you.
Bruce Allen at Marketing Catalyst had a recent post that offered some real down to earth advice on following up on face-to-face meetings. First, pick just a few cards from your stack, in fact he suggests three per event. Then, email one, send a handwritten note to the next, and telephone the third. The message can be about your conversation, or simply that it was good to meet them and that you hope you can get together for lunch, or whatever. Better still, go ahead and try to set the lunch in your communication.
I’m not sure I would limit the contacts to just three, but Bruce’s point is valid. The number isn’t important, it’s whatever works in motivating you to actually follow up.