Have you ever been to a networking event and there is a guy going around the room handing out his card. He'll come up to you, say hi, ask your name and hand you a card.
Don't be that guy.
Relationships are not built on business cards. Cards are a handy way to share vital contact info without writing everything down. BUT the relationship comes before the card. If you are in a room of 100 people networking making 2 or 3 good connections is much more valuable than handing out 100 cards to strangers.
Do you know the people you give your card too?