Go read the magnificent Cat Rambo on panel moderation. Of intense interest to me as the first panel I was ever on I got to be the moderator. Yes, that story will stick with me, "wounds we carry" and all. Actually it wasn't that bad. Fortunately I was prepared and I had the benefit of watching some excellent panelists (of whom Paul Melko stands out in a fabulous crowd; he's quiet, he lets other speak, and he comes prepared with notes and when he does speak, he is entertaining). But go and read Cat's list before you are doomed to sudden moderator unpreparedness. I can be a deadly disease.
And while I'm thinking on it, when at a con, and have become somewhat known, always be prepared to be hijacked. Just ask Dave Kletcha about sudden panelitis.
And there are various pieces of advice for panels. Like, "If you find yourself on a panel with David Hartwell, introduce yourself politely, make a general statement, and then sit back and watch the master work, don't worry about participating too much." I've never really liked that advice (although I like David Hartwell very much, he's a cool guy and if you get the chance to talk with him, about anything, you should take it). See, that's what a GoH's job is, and that's why they panels all to their lonesomes. If you're on a panel, speak up. I had the opportunity to be on a panel with Cory Doctorow called "Big Brother." Yes. Cory is all about the civil liberties and the man knows a lot about the subject. But if you want just his take on it, you can read Boing Boing and get that. I doubt anybody paid the admission fee to the con to hear me hold forth on the subject, but just conceding the panel to one guest, to me, is a bit like shirking ones responsibility.
And some more on attending cons by Faith Hunter over at Magical Words. Although I'll say for point one on what aspiring writers can get out of cons, avoid making the pitch unless asked to do so, but yes, try and sit at the same table as an editor your respect and admire (and as an aspiring author you should start to know editors names). And meet other writers. Seriously. It's the best part of the convention (well, at least for me).