No more address books. No more contact files. Here's something I've been doing for years. It's a way to organically grow your networks online, increase ambient awareness of people you've run across in person, AND keep entropic clutter to a minimum. Take that inert stack of biz cards on your desk. You're hoarding them to contact those folks when the need arises, or when all your ducks are in a row, or something. You're waiting for the day the cards will work -- but don't wait.
Find and connect on (multiple) social sites with each of them. Toss the cards.
Believe that you will be able to find these people without the physical card. Believe that you don't actually need their phone number or fax or street address -- it's all findable!
(Flipside: make your own contact details findable by the people you want to be found by. That's a settings issue at your profiles.)
Know that by connecting* with these acquaintances ambiently via online networks, you're taking a small action that will help bring them closer for mutual benefit now, and in the future.
You're now starting to use social platforms like a web-wide contact book.
*And if you freak at the thought of requesting a low-pressure connection online at the most appropriate sites, then how were you intending to reach out to this person in the future when you actually have something to ask or propose?