Authors are encouraged to establish an "online presence" these days, and that typically consists of some combination of a Facebook page, Twitter, and a blog (not always all three).
I think Facebook is the most difficult of those three to do well, because it takes a lot of effort to maintain the multiple types of media (photos, videos, wall posts) needed to make a Facebook page seem active, and also because it's hard to find the tipping point where your fans start engaging with your page and sharing it, which gives you viral marketing, which is where Facebook outpaces all other social media platforms.
How have you been using Facebook, if you have. What's been the best and worst part? Are there any Facebook pages that you think are really getting it right?