When I read this post by Jason about his family's experience flying, I had to wonder if airlines' relatively new practice of letting people check in ahead of time online could cause problems for those who actually show up on time at the airport. From Jason's post:
So my family sat around for two and a half hours to fly standby on a flight they booked months ago and and got to the airport for in more than plenty of time. They sat at the gate and watched people show up more than an hour later than them and get seats, no problem.
I haven't had this happen to me yet, but if it did, I'd be pretty ticked about it, too.