The best is when it has GPS but spotty cell service and you miss a turn because "turn right onto $longname $state $many_syllable_route_number" is actually a yield that doesn't require you to stop and you need to turn left/right onto $other-street before it's done telling you to do what you just did. Then it tries to re-route you but 3g service is too spotty to do that but not to spotty to get so far along in the process that it discards the old route you just made a U-turn and got back onto.