Something that has not been mentioned, you need to be very nice to the agents as well as do not sit at the desk asking if you are going to make the flight or keep going up to the agents to ask. We always tried to be discrete and extremely polite. (Sitting away from the counter)
As most have said it is a great cost savings on the tickets but, you can loose a day or more waiting on flights. The only time I enjoyed it was going to London over a New Year's Eve in First everything seemed great until we tried to come home. The flight before ours was cancelled and they were placing all the pax from the previous flight on to ours. Needless to say 8 hours at LHR was not fun as well as explaining to my boss why I was not able to come in to work due to the flight.
After several other problems with passes I decided to spend the money on tickets rather than all the hassels of the pass.
Buni