Well, Gary said to post your feelings about the Montreal meeting, at 2am, I can't think of a better thing to do! The meeting was huge, it took me awhile to adjust to the way everything worked, and realize that while things were supposed to be timed pretty well, they sure weren't.  I presented at it, and it wasn't nearly as intimadating as I thought.  I suggest that all the undergrads that can should give it a shot while they still can do the undergrad session, since its a good way to get into the swing of things.  
Also, on a side note, the SPS food was wicked good, and cruising the vendors was a great time.

charlie here, tellin ya'll that march aps 2004 is off the hizzook!

All in all, I'd also recommend checking out one of these conferences, not only for the wicked food and experience of spending a few days in a different city, but also (believe it or not) the educational experience.  Attending a bunch of talks (say, a dozen or so) will both make your brain swell and give a sense of how good science is performed, whether it be theoretical or experimental physics.  Also, if you're not sure what you want to study in graduate school, it's a good place to see various topics in action, as well as make contacts with research groups across the nation.