Banning Facebook is like banning the telephone. What people in authority don't realise is that it is just a tool. Any tool can be used or misused. What they should be focussed on is harnessing its potential not being paranoid about what people do with it.
Facebook, like so many social tools, is actually primarily about learning. Yes learning what people had for breakfast - but also learning news, learning what works, learning what books are best to read, learning where to find the right bit of information.
It is particularly ironic when schools ban Facebook as they are the very ones who should be teaching effective use of this technology - not keeping their pupils stuck in some industrial, factory model of learning.