Traditional business cards and CDs-as-business-cards are dangerous because:
1. They assume old-style communication: I have a message for you.
This is a transactional view of communication. If you simply put your card in someone's hand as a way of marketing, chances are it will end in the trash can when your back is turned.
Good reading from Seth Kahan to jolt your Monday. I'm using a card these days as a convenience to others. I know I can't write my contact info clearly; I fear I can't articulate clearly in speech. What I wish I had was a reference to my blog--that would provide a way to continue the conversation.
And check out this post on Lifehacker, which proposes another use for "cards."
An event card is exactly like an old school dance card. But instead of scheduling dances with pretty people, you'll be marking off successful connections with your targets. The simplest version is a plain list of names. That'll work if you have an amazing memory and ability to place lots of new names with faces. But most of us aren't so gifted.