I have been a USA cycling member for many years and have been able to use the code on every flight booked within the calendar year. As the 2014 license code will be good for only UA flights in 2014.

Usually it is about 5-10% off, I have never seen any more or less taken off the price.

PMUA started this program and as mentioned above did give vouchers for bikes to be checked for free ($100 value today). I still have a few from the early 2000's, considering bringing one to a agent on my next flight and seeing if they will take it or not! It has the tulip logo on it and states its good for any domestic "United, United Shuttle or United Express flight in the 50 States"