I agree that you will always find people willing to help out and let you plug in, but bearing in mind that some of these things can take hours to recharge, there is an element of risk leaving your expensive gear attached to someone else's leccy supply. (even if they themselves are honest you might be kinda putting them in a position where they feel responsible for looking after your gear). I suppose a long extension lead might sort that tho!
At least with an in car thingy you can lock stuff inside your car while its charging.
Not wishing to imply that the place is overrun with pikies, but better safe than sorry.
F