I've got a hunch that someone out there has started a listing of unattended, hot AC outlet locations. Sort of like the "wardriving" WiFi lists.
Back around 2004 or so, two of those glorifed golf cart type plug-in electric "urban cars" began appearing in my office building's garage. The drivers would arrive very early and park in the spaces by the wall outlets. After a month or so, the weird little cars were no longer seen.
One day I mentioned it in passing to one of the building maintenance guys, who informed me that the management had noticed it too and they killed the power to those outlets. It wasn't so much the electricity cost (a drop in the bucket, in those circumstances) as it was the fact that the drivers didn't ask permission or offer to pay. So, no more electricity for them.