@quixoticgeek My only related complaint from SF is that the different transit systems, which interconnect, expect different things as far as tagging on and off.
BART: you must tag on and off, through a gate.
MUNI: you must tag on, but not off. If you board muni at a subway station, you must tag on by passing through a gate. If you board at street level, just tag on at the door. If you try to tag off at one of the fare gates when exiting a muni subway station, the gate will not respond, and you will stand there blocking traffic while you wait for confirmation of an ignored transaction.
CalTrain: if you tag on but not off, you will be charged the maximum possible fare for a trip starting from your point of embarkation. There are no gates, so please just remember to find a post. (I usually remember once I've exited the platform and have to go back, up and down some stairs or escalators or elevators with my cargo bike.)