The seemingly innocuous Like button recently spread from Facebook to sites all over the web as part of Facebook's Open Graph program. You read something on some site and you have the option to like it and see who else liked it.
That functionality is part of a grander scheme, more details of which emerged today as Facebook introduced Open Graph Search. This is search functionality where the more people Like something, the higher it appears in search results. It's a whole new form of search engine optimization that places Facebook, and it's insistence upon the dawning social web, in competition with Google, Yahoo, and Bing.
I think this is huge. It puts the rubber on the road for Mark Zuckerberg's grand plan of the web being a social place. It posits that opinion and not math will be the fundamental driver of finding things online.
From an immediate "what does it mean for me" angle, it means that everywhere you turn, someone will be urging you, begging you, to Like what they've posted online.Â