I use Facebook extensively and in my experience, it is well worth the time investment with one caveat: don't count on it generating instant revenue. It took a good, solid year before I started seeing any kind of financial return. It did help to increase website and blog traffic earlier than that but only at marginal levels.
I've made several print sales to folks who "like" my Facebook page. Where it is most lucrative for me is in marketing my workshop and guiding services. In the 2+ years I've had a FB business page I've secured at least a dozen guided/workshop clients as a direct result of my participation on my FB page.
I've noticed a "snowball" phenomenon with FB. The more "likes" you have, the more of them you'll get. The more "likes" you've got, the greater your exposure. It takes time and effort to build a following.
Here are a couple tips that have helped me to build a loyal and engaged following: Use your FB page to engage your followers. Ask questions, interact with them, have fun and for God's sake, don't try to sell to them all the time. Every once in a while is fine and to be expected, but if you're constantly trying to sell to them they'll split. Stay active, but not too active. Post new images, new blog posts, etc. A few posts a week seems to be plenty. A few posts each day? Too much. Be genuine, be yourself.
I hope this is somewhat helpful. I'm certainly no expert but I've got a decent following (over 1,600 likes) and quite a few very engaged and interactive fans. Have fun with it!