Ive posted my thoughts on them on a number of occasions Ian. They aren't effective marketing tools IMO.
You say FB will be big. It is, but it isnt a big marketing tool. Just because something is big doesn't mean it is the big thing you want it to be. Its a big playground. Thats it.
Canvassing always has been the main 'stream' for new work and will be for the next 20 years. Ill stick with Google, nothing has changed with profiling on Google essentially in the last 10 years, I predict they'll still be the market leaders in another 10.