I think facebook is a wonderful thing for some people. I love facebook – I can see pictures of my friends and what they are up to, keep in touch with many people on the quick until I have time to really speak to them. Its great.
Everything on the internet is a potential waste of time (YW included). I do find it a little ludicrous when people who use the internet decry others for things that they dont use (so long as they dont violate halacha). We all have to make choices in life and learning to make good choices is better than cutting off everything.
That being said, my step-nieces use facebook in a non-kosher way. They are young teenagers who would benefit from not having access. At this time, there is no real way to keep it away from them (they have no internet at home anyway – its used at the library or other peoples houses). It would be better if their parents would allow them access and monitor them.
I think many people forget this generation is MUCH more tech savy than most of their parents…