I don't need to introduce you to Facebook. What you might not know, though, is that a lot of businesses, including lawyers, are using Facebook to create fan sites for their businesses. You can tie in a bunch of other tools (like Twitter, blogs, and other media) into that site, and some people are even using it as their main business website. The question is whether you should hitch your wagon to that star.
Facebook undoubtedly has its benefits. There is a huge traffic draw to that site, and users who already have a personal presence on the site can be very successful in attracting followers, or "fans." The compatibility the site has with other platforms is also very helpful. However, just a few years ago Facebook was a distant second to MySpace (remember MySpace?), and Twitter barely existed. I worry that devoting all your resources to Facebook may be a problem if Facebook users abandon the site for the next big thing.