I leave my cell phone number on the dash if there is only a few available chargers in the area.
There is always that chance that someone else has an emergency to tend to.
Yep. I left a note on the dashboard when I was in the "one and only" charging spot in the garage I was in, saying "If you need to charge while I am plugged in, call me at XXX-XXXX-XXXX".
Of course, I arrived to find that I'd been unplugged without notice by a Volt.
I managed to actually meet the Volt owner later, he apologized for not looking at my dashboard and then asked a lot of admiring questions about my car.
- - - Updated - - -
Yes, yes! Unless an abundance of charge stations arise (doubtful, I think battery tech will improve faster), don't use a charge station (or worse, merely occupy the space) just because you can. Leave it available for someone who needs the charge!
In the bitterly cold weather on my road trip (down to 5 F), with unplowed roads and appalling mileage, I started charging whereever I could just to fight the vampire losses from battery heating, even if I didn't "need" it. But I left a note on my windshield, as noted before -- if someone else needed it more, that's fine, I just would like to know what's happening.
- - - Updated - - -
There are other issues at play here that add confusion to the issue. In some jurisdictions EV parking is provided as incentive to get an EV. Another is availability, for example in the Northridge Mall there is one charger yet two "electric vehicle" parking spaces. Clearly they aren't requiring vehicles to charge in order to park.
Actually, I think it's generally a good idea to have extra spaces per charger for the following reasons:
(1) insurance against ICEing
(2) Charging, but parking for *a longer time* than you are charging, which is perfectly reasonable behavior, especially since charging time can be unpredictable. If I'm parked at a charger but I'm *done*, I would be OK with someone else pulling up in the next space and taking the charger, but I may not want to hike back from whatever store or restaurant I'm at right that minute.