My car just went into Tesla for its yearly maintenance; the service is recommended once a year or every 12,000 miles. My Roadster had around 9,000 miles on it.
The service included a general check of the car, battery, tires and an update to the firmware. They replaced all my HVAC knobs. The original versions were poorly made as I reported earlier. They also replaced the floor mats with a new model that has a hook attachment and is less likely to shift around.
The service costs $600 under warranty. I was a little disappointed with the cost of the service. Since electrical cars are simpler in design, the maintenance costs should eventually be cheaper than a gas powered car.