Facebook is said to be looking at ways to turn its “like” button into a multi-million dollar bonanza.

The feature, which is currently used simply for giving a thumbs up to user content such as status update, could be the key to breaking through in the contextual advertising market.

The company wants to make it possible for websites to put a Facebook “like” button on their pages, similar to those which many already make available for social media sites such as Digg.

While a user “liking” a web page could publish a link on their profile and act as a form of promotion for the site — as already happens via a “post to profile” or “share” button — , it’s got a more valuable potential use for Facebook itself.

Though the company has said “we have no announcements or changes planned to our ad offering and policies”, there’s a strong suspicion it would like to use the data from the buttons to learn more about individual users’ tastes and interests, further refining the personalized adverts it shows users when they log-in… and further increasing the rates it can charge advertisers for ever more targeted advertising.

It’s notable that the scheme would require users to specifically click on a Facebook-branded button, which means they shouldn’t be surprised when the details appear on their profile. That’s in stark contrast to the much-maligned Facebook Beacon program which updated user profiles with details of activity on partner sites such as when they ordered a book or CD from an online store.

In that situation, Facebook’s biggest blunder was making the scheme opt-out, meaning users, whether or not they knew about it, were enrolled by default. To make things worse, the scheme launched just in late 2007, meaning some users surprise Christmas gift purchases were revealed to the recipients.

It’s not just Facebook which will come under scrutiny from the new scheme, though. There’s also a possibility that the websites displaying the “like” button will use the details for marketing purposes. After all, it’s one thing to know somebody has visited your website, but quite another to know exactly which pages earned their approval.