Heck, I just tuck in behind Charles. He creates a gap and I go through. Kind of like a blocker in football but he stays in front
Last year I was frustrated in the half but the full was fine. Yes there are thousands of people but that is what makes it such a fun race.
Try to start in the right corral and like others said do not spend too much energy passing people. It is so easy to take that burst of speed to get around a few folks. You'll pay for it in the end though.
enjoy,
Duane