I haven't had too much opportunity to deal with the A.I. The battles I've had with a full party have been relatively easy, so I haven't had to keep too close of an eye on them. The battles happen pretty fast and there's a lot of room to move, so most of the time I have no clue what the other two party members are doing.
Just make sure to listen to the directions that your party members give as far as directions go on the world map - I've taken a path that I shouldn't of, and got my ass beat into the ground like in that PA comic. When you're in over your head (or facing more mobs than there are players in your party), the weaknesses in the AI quickly show.