Had to have some work done on my wifes car. Dropped it off at the dealership, got a ride home by the shuttle (retired guy in a mini van).
So, what’s the etiquette on this? Is one supposed to tip these guys, or what? 
Not unless he ran errands with you. No tip is needed or expected.
My rule of thumb is that if a business is provided an extra service that they don’t charge you for, I tip; ie., if I go to a computer store for a new heatsink or something and the guy offers to install it, I tip.
When I was in a similar situation, (dropped car off in the A.M., got ride to work, got picked up at the end of the day when car was fixed), I offered the driver a tip in the morning, and he was right on time when I needed to be picked up. He said he actually liked doing the shuttling, though; if he wasn’t doing that he’d have been doing mundane things around the dealership like washing and vacuuming cars.
ETA: He didn’t take the tip. And he was a regular full-time employee, so presumably he was being paid a normal wage. I think the times when it’s crucial to tip is when (a) you’re being provided a personal service and (b) the person providing it is dependent on tips for a goodly portion of his/her wage. In this case if the person had, for example, simply cleaned up the car after the work was done, he wouldn’t have gotten a tip, so he really didn’t need a tip for spending a part of his workday doing something else.
I agree that no tip is required or expected. There’s nothing wrong with it if you want to, though. I would say the same for airport shuttle drivers of rental car companies, if they handle your baggage. Some people must never be tipped (flight attendants), some must always be tipped (waiters, except in case of bad service) and some are in between (shuttle drivers).
I wouldn’t tip, but I always give a buck to the airport guys if I use em. The difference is I’d be payin’ cash for the shuttle, so I’d have bills, while I wouldn’t have any cash at the dealership because I’d be using my card.