9 times out of 10 getting in one and driving it around is just an invitation to get blown up by an enemy rocket launcher. Even if by some celestial chance you last more than 10 seconds without exploding, being in the passenger seat will get you killed most of the time since you're a sitting duck and most classes can't equip a weapon short enough to shoot while in the truck. Getting in the gunner seat is basically a death sentence. All somebody has to do is aim slightly above the gun sight to get a headshot on you, which is difficult to play against because of how narrow your line of sight is while in the gunner seat.
In all my time playing the beta, I rarely saw people use the truck. If they did, I never saw them accomplish anything meaningful before an enemy RPG signaled their doom. Right now, it seems like the only use for trucks is as a big, flashing sign for the enemy demolitionist that says "Shoot me for some easy kills".