When I took the business basics course at Niagara College I learned a very important lesson from Larry Bitner [ http://www.larrybitner.com ].
He said that it is far more important to collect business cards rather than giving some.
The reason is that YOU are in control. You can decide WHEN to contact the person.
When you give your business card, yes, you feel important but you rely on other person's schedule to get in touch with you.
What if they loose your business card or what if they are not organized enough? In some cases it may be hard to get that contact info.
Bonus Lesson from Larry Bitner: Make sure you always have business cards with you. Also make a habit of giving at least one business card per day to a potential customer.