I suppose part of the problem is that everyone expects immediate returns from networking. While that may rarely happen, networking is more of a long-term investment than that. You're not going to get a job offer because you chatted with someone over a buffet table. But they may remember you when it comes time to look for abstract reviewers.
Or, if you're bold, you can follow-up when it makes sense. Quick examples - when an assay doesn't work, when you have an interesting piece of data that may fit with someone else's data, when you hear information that may be interesting to someone, when you like someone's talk. I have sent video links that stemmed from a conversation I had with a Nobel laureate about my kid's education. I've sent information about new aquariums to members of the Academy, and corresponded with Senators about healthcare reform. I've also emailed an NIH director I met at a workshop wishing him luck when he announced he was heading back to academia.
Remember as you network that everyone at these meetings is looking to make connections. They just might not know that they want to connect to you. Your job is to be nice, humble, and honest. If a connection happens, it should be organic and not forced.
Which is also why I never look at someone's name badge until AFTER I start talking to them. Yes, I talk to the old guard. But I also talk to their trainees, their techs. I've even gotten information about grant opportunities from conference security. My approach to networking is to gather information, but also listen to what people are saying. I never ignore people and often start working a room by chatting to someone who is acting like a wallflower. Many times they appreciate the gesture and open up. Or introduce me to their friends.
I am fearless in what I'll go to - I've gone to conferences as the only representative from my university and have no problem being in a room where I don't know a soul. Strangely, some of my best personal and professional contacts have come when I start the night not knowing anyone, but end the night dancing at a bar with a group of new friends. Most importantly, I'm not shy about asking for, and listening to, advice from those that have come before me.
And you may even benefit professionally.