I don't think a facebook presence if obligatory, but really is well advised if you want to reach a portion of the net-using public that sees facebook as _the_in

I don't think a facebook presence if obligatory, but really is well advised if you want to reach a portion of the net-using public that sees facebook as _the_internet_. If you skip FB, you're skipping a lot of eyeballs potentially. If you get those eyeballs, it's up to you to keep them interacting directly sans-facebook afterwards.