Good question, one I have also wondered about. I do have a personal facebook. In real life I am an RN, and have a very large circle of friends, both professional and personal, and I think that if I posted author updates to my personal page, it would generate a lot of sales. Just yesterday at work, I mentioned to one of my close friends that my book was for sale, and a few other people overheard us talking(who I am not facebook friends with), and it appears I sold 15 books last night. I can't say if those were random web sales, or from my work contacts, but I think every little bit helps.
That said, however, I did make an author page, just because at this point I am not quite comfortable yet with putting myself out there. I do not want to feel like I am spamming people on my personal page, if you know what I mean? (Of course, my new page feels lonely right now, hopefully it will grow haha)
So I think FB is worthwhile. Good luck, and make sure to post a link to your page so I can "like" it.