I love it - I've got in touch with folk I was at school with, keep in touch with folk I worked with, see folk from TAS, see businesses I'm interested in (and not) and "met" new people
It doesn't replace "real' friends but I have made FB friends that have become real friends, bit like TAS in some respects.
There's some crap out there, on FB, TAS and real life but you just have to filter it out.