>  I have no reason to call them

  Networking (, The art of) is not an endeavour you always undertake for immediate or medium-term gain. You don't need some life-threatening emergency to reach out to someone. LinkedIn, through it's endorsement and sharing of articles gives an easy way to stay on a contact's radar for no cogent reason. Think long-term. I presume you're familiar with the HTTP protocol as a developer. You know what happens to a HTTP session when the user doesn't do anything for a while? It dies. And this is what will happen to all those links the business cards and chin-wagging you engage in at conferences. You need to find a way to chip in a hello (read: ping) how's the state of "The Business"(whatever that may be for your contact) every couple of weeks/months or you'll just fade into the ether.


> I can't remember the faces to the names, nor most of what we discussed.

This is your problem then. To sort this out, I'd recommend you start by striking up conversation on something you're actually interested in. Not B.S-ing your way through a topic or subject you couldn't give a flying dutchman about. Also pick your targets carefully, in the same vein. 3 business cards from people you actually have stuff in common with will serve you better (and be easier on your memory) than a fistful of business cards from people you barely have anything in common and you're going to forget as soon as you turn heel.

>I never seem to meet anyone who can help me with anything

Again, think long term. And try not to be grabby. You can't expect to mine a contact for all possibilities after the first meet. Typically you'll only get to second base after the 2nd-3rd meet. Impatience sets in when you're expecting short-term turnaround on a contact (see my first point) and you have too many of them in the first place. Pace yourself and invest yourself in someone you have a solid link with.