I went to Heathrow Terminal 5 the other day. Here are some observations:

1. Cool: The short stay car park has a camera at the entrance barriers which reads your number plate and prints it on your parking ticket moments later. (I wonder if they've had problems with ticket transferral in the past.)
2. Expensive: A one-hour stay will cost you over £6.
3. Annoying: There is no passenger pick-up point. Just a drop-off point. The signs for "pick-up" lead down a one-way route to the car park. If you want to pick someone up, arrange to meet them at the departures drop-off point instead.
4. Confusing: The international arrivals area has two gates from which passengers emerge, separated by a good distance. There is no indication of which side a given flight will emerge (and it is not clear if this is even deterministic). There is no single area through which all exiting passengers pass through. There is enough curvature and pylons in the layout that, at even a moderately busy time, it is neigh on impossible for a single person to monitor both sides simultaneously, even with a lot of constant side-to-side neck twisting.
5. Useful: Now that they know your number plate, next to the pay machine there is a "find lost car" machine to help you find out where you parked you car! I should have tried it to see what kind of granularity it works to. I'm not sure if they continue to use cameras throughout the car park to track your location, or perhaps they have an embedded RFID chip in the parking ticket.
6. Practical: Checked luggage was delivered to the passengers!