facebook is the largest single collective of human beings and related information ever assembled in one place in human history... This should make it the best markering and member resource on the face of the planet...... but you try to actualy get the attention of any facebook member for 3 minutes to show them what your site has to offer... In truth, users on facebook are more interested in posting photos of what they had for breakfast, of shring chain letters to with cliche images of angels and see more of increasing their own sence of importance in the world by dictaorialy controlling their Fan page.

Stripping members from fb can be done. I have to it, but it is difficult, and facebook itself does not make things easy. If you have a page and you message all fans of your page with offers or links then you will get banned or suspended for spamming. If you keep adding friends at a high rate then you will be suspended for spamming or banned from adding friends. I have had several bans over tha past few months.
Fb ads are cheap... or free if you find a voucher. They do get hits, but you will not get conversions unless the page you take them too is enticing enough. It is worth a try with a free voucher.

Join groups with similar interests to your site, and drop FREE membership codes into it. We have had good results with this.

If you have a welcome page on FB then you can include flash on that page. We have a interactive welcome page with promo videos of the site, and a FREE membership code generator, that generates a FREE code and takes the user to our site.

There are meany ways to use and exploit facebook, but at the end of the day you are trying to change a socialy induced mindset that has grown over many years, and that is not going to be easy.