Be careful here, you are talking in absolutes.

If you are b2c you should definitely take a close look at facebook as a part of your marketing strategy. No, not for your friends / family but so you can pay for targeted facebooks ads to show to your potential customers to get them to like your page.

My startup now has over 35,000 'likes' on our facebook page, all in our target demo / market. This is huge. We now have a captive audience we can market to. I would put this just as high as building an email list and consistently marketing to that list.

YES it drives revenue, and more importantly awareness.