Cabinetsanchez over on LJ has documented something that I saw in action yesterday while running a few instances -- while it's a ton of fun to run my Crashin' Thrashin Racer around (I'm undefeated since I picked up the achievement the first day I got the toy, by the way), players have found a few extra ways to make the Racers work for them. Yesterday, I saw one of my group members using the Racer a few times to scout the instance ahead and see what pulled with what, and as CS says, it worked great: while the Racer will aggro enemies, they won't tag on to the rest of the group -- they'll just reset after they destroy the little car.
CS also says that the Racer takes no falling damage, so you can send it exploring off of cliffs and platforms, and he says that though the car is considered level 60, its aggro range is pretty small (I can attest to this, as we were driving it pretty close to enemies yesterday without it registering on their radar). And he's got an even more devious use (some might say this is an exploit): bosses aggroed by the racer will sometimes despawn after they conquer it for up to 30 seconds or so. That seems like a hotfix waiting to happen, but I haven't personally tried it, so it may not be as useful as it sounds.
The downside of this is that the Racer was meant to be a fun item, and if it really does lead to behavior that Blizzard considers exploiting, they might have to think twice about including great items like this in the future. We'll have to see what their ruling on this is, but hopefully no matter what happens (I'm guessing a quick hotfix, maybe even shrinking the range of the Racer's controller), this won't prevent Blizzard from giving us more fun toys later on.