Showing up early is good. Some of the dealers will hit the other tables before the doors open and try to snatch up the good stuff, then put them out on their own tables before most of the public gets through the doors.
There's usually a mix of private collectors with their estates (like me), retailers like Pipes2Smoke with their tables FULL of new pipes, individual carvers with a half dozen or so of their own creations, tobacconists with free samples and just about everything else you can imagine.
My advice is to take it slow at first. It's hard to focus on an individual pipe when you're looking at a table of several dozen pipes laid out. Don't be afraid to ask "is this the best price you can do?" as most are willing to make a deal. The selection is, of course, best in the early hours but the prices are best later on when guys are more willing to give you a better deal rather than take their stock home.
Some of the bigger retailers will take plastic but will give a better deal for cash.
They draw raffle tickets every hour, but they wait until the very end to raffle off the pipes so stick around if you're feeling lucky.
Personally I enjoy talking to the carvers. They're usually happy to just chat about how they make pipes, where they get their materials, and just shoot the breeze. I know Scott Thile, Michael Parks, Wayne Teipen, Thomas James, Bill Shalosky, Tim West, Dr. Bob Keiss, Russ Cook, Joe Skoda, Ian Walker, Joe Nelson and others will be there. These guys are rock stars. It's like being able to hang out with Bono or Springsteen for an afternoon.
But most of all have fun!