Surely this could be the most deadliest enemy the Doctor can face - i.e. if he were to accidentally come across them again in the future without the little wrist band thingy?

when amy and rory realised the doctor have given his wristband to amy, they wondered about the doctor himself, and amy then said something along the lines of "of course, timelord, probably dosen't even need it" so I think that implied it couldn't effect him personally. although It would alway's be a danger in the form of turning his companion's.

Good point - I'm re-watching the asylum right now so will tell you in about 20 mins.

Not wishing to stir up a hornets nest, but maybe 11 just thought he could regenerate and was doing a Peter Davidson style sacrifice ...