Quite, Andy, although I still think that any teachers added to their pupils' facebooks, etc., are making a mistake because it can lead to a clash between two lives that ought to be fairly separate. Facebook can be a scene for unwanted drama, although really it's just a reflection of the drama that existed anyway, and the only difference is that everyone can see it.
The point, really, is that in a teacher-pupil relationship, it ought to be at first up to the pupil as to whether or not s/he wants to know the teacher outside school hours, and then the teacher should have the judgement necessary to know whether or not that's appropriate in the case at hand. We shouldn't be too dogmatic about it, I don't think. Most pupils anyway won't want to befriend their teachers, so it rarely comes up, but I'd have thought that the ideal teacher is someone you actually like -- someone who doesn't force respect, but has earned it; someone you might even want to get to know better. (Oh, and also they have to be teaching the material correctly, which is overlooked surprisingly often...)