Just look at the conference as a few days of hanging out with like minded people. Just have fun.
My conference knowledge is limited to three years of PyCon, the annual Python conference, but maybe it's helpful...
* Sit in the front row. You paid to be there, you probably traveled to be there, and you probably came because you wanted to learn something. Sitting in the back posting on HN is easy, but get up front and suck the brains out of the speaker. I like to write notes with pen/paper and save my laptop for later.
* If you liked a talk, go up and thank the speaker. Introduce yourself, maybe ask a quick question, then let them get on their way. You might have just found an interesting person to have dinner with when there's 500 random people in the hotel lobby trying to figure out where to eat.
* If no talks interest you in the given time slot, go roam around the hallways, the expo room, or grab a cup of coffee. See what people are up to -- everyone's there with a common set of knowledge/problems. I've learned a ton just from introducing myself to the other guy getting a cup of coffee and end up finding out he also works in the same field, doing the same stuff, we both know each other's companies, but we're solving our problems in totally different ways. Rather than killing time on the web for 30 minutes until the next talk, I just made another acquaintance to grab a beer with, and he made me think about what I'm doing at work.
* If there are development sprints, stick around and hack with people. At PyCon I believe we had 400 people the first day, and it was some of the most fun of the whole conference.
Just talk to people. There are tons of interesting and friendly people at conferences. Even if you are shy or don't know anyone, just remember (especially at tech conference) a lot of the people there are just as shy/uncomfortable with 'networking' as you.
