Firstly I am not qualified to practice law in US so this is not a legal opinion.
However I can give you some case law on how courts have (sometimes confusingly) seen links. Basically the problem with many "free" services is that they need to monetarise your eyeball. In the past, courts have ruled that
- deep-linking of content (no-no) where you have the page from deep inside a site come up in a frame with your ads surrounding it
- shallow linking (maybe OK) with attribution (or disclaimers) where reference material outside one's site
- a link by itself is not protectable as such (legally speaking) but it is common courtesy to observe the robots.txt for search engines.
The whole technology of links and suchforth is actually giving rise to a new form of intangible property. How much is a "recommendation" worth. Are facebook "likes" have economic value outside of Facebook. Paradata (see my thoughts in www.knowledgerights.org) is basically the foot-prints or impressions left by other people, it's like a herd of cows wandering through a meadow. Eventually a beaten path to the best waterholes get mapped out (eg tag clouds). So who owns that path, the site hosting the waterhole or the people who trod that every day? You can see the problem if there are 2 or more waterholes. So what you are proposing is to erect a kiosk on the side of the path, how close you are to the waterhole is a matter of conjecture as Facebook obviously wants to license out their datamine of recommendations and user "suggestions" (whether artificially prompted as in your case or not). I'd suggeset focusing on your own robots.txt (which you have legal rights to control) and follow conventional practices wrt Facebook. See what others are doing because law is also crafted by social expectations.
The legal system is barely keeping up with software patents, I suspect SNS to come into litigation at some point in the future as more search engines and such forth emerge (see recent CraigList lawsuit against mashups). If you're not too visible and is seen as a complementary service, the legal risk is reduced (but not necessarily zero).