Hrm, if I had more time on my hands and some one to go with me to chat with, I might do it just for the experience (my roommate doesn't understand this at all... he is of the just get it when it's easy to get mentality and thinks people who line up are just doing it to be first. Maybe some are but to me it's more about experience).
Ok, my cons first:
Getting no sleep, groggy next day (hope yuo don't have to work/go to school), all that time just sitting in line (this is why I'd do it if I had more time on my hands and some time wasted would not be a big deal).
Pros (not that I've waited for an iphone but it was kinda like waiting in line to get concert tickets when I was a kid):
1. It's fun waiting in line for something you are excited for.
2. As people said, you get to chat with the people around you, it's a social experience.
3. It builds excitement up for what you are buying. Makes it more fun.
4. If you have friends to go with it's fun to get all excited together about what you are waiting for.
Anyways, it's not for everyone (my roommate thinks I'm crazy when I say I think it might be fun to camp out for the iphone just for the experience. I say I think it would be fun but with my time these days it's not worth taking my time to do. Plus I like sleep, heh. I think I'm just getting old honestly).