I noticed an interesting behavior when I have longer stretches of going downhill and using regen to put in a good amount of energy back into the battery. As I was going down I kept an eye on the trip meter which keeps track of the energy in kWh. At the bottom of the hill I saw 0.7 kWh where added from regen. That would roughly be 2 miles. The Model S doesn't add these to the range, though. The rated range number did no change. It stayed as it was before going downhill. What's interesting, though is that i was able to drive about 2-3 miles (at 300 Wh/mile) before the number decreased. It seems the energy gained through regen isn't added into the rated range in terms of the numbers displayed, but of course the energy is captured and available.