When I got to the Pittsburgh airport today, I was shocked to see how long the line for US Air was for an early Sunday morning. It struck me that airports could offer a really nice service, which is to provide an estimate of how long the line will be at a given time, both for check-in and for security.
I don't think it would be that hard to implement either. Airlines already know how many people should be checking in, and they should know the rough rate at which people can be processed. For the security line, you just need to aggregate the number of passengers across all airlines. Afterwards, calibrate your data (ie fudge the data a little) so that the numbers match reality.