This is almost certain to become an issue when the number of EVs grows to a substantial percentage of the market.
We tend to regard public outlets as fair game when it comes to something like charging iphones or running a laptop. In these cases, the amount of power is trivial and not worth the hassle of making arrangements for payment. People may be tempted to transfer that reasoning to their cars but it doesn't transfer readily.
Charging an EV is a very different matter. We're talking definite and tangible cost. To take $.50 or $1 of power without permission is clearly not justified. The situation in AK with block heaters may have evolved to become a social norm because it's in everyone's best interest. Not so sure that will translate to charging EVs.
I'd consider it equivalent to asking for gasoline. If you were running out far from a filling station, would you just walk into the garage of a home or business and help yourself? Probably not. You'd look for a way to ask permission, offer payment, etc... Only as a last resort would you simply take, and even then you'd leave behind a payment if possible, your name and number, etc... Why would it be any different with an EV?
I definitely think you'll be reading of problems in this area during the awkward period before a robust charging infrastructure is in place.
http://www.thelocal.de/national/20100901-29557.html