This superb article on GigaOm really puts into context what Facebook is doing. Google's search evolution was two stages:
1) Realize that the links that people create on the Web are a vote about the value and subject matter of websites ("hubs and authorities", aka PageRank)
2) Realize that the clicks that people execute on Google search pages are a vote about the value and subject matter of websites (machine learning on clicks)
and then organize search results according to the composite of the value indicated by those votes.
Facebook is now re-executing stage 2) and moving to stage 3):
2) Capture clicks via toolbar integration on websites and do Google-comparable analysis
3) Realize that "like" and other social actions (forward etc.) that people execute on the Web are a vote about the value and subject matter of websites
and then organize recommendations and exposure (in the Feed, etc.) according to the composite *personalized* value indicated by those votes.
Facebook is truly turning itself inside out with this move, and may re-shape the web around itself, in the same way that desire for "Google Juice" has re-shaped the web as we know it today. The beta phase of social networking has ended, and the real product now emerges. This is going to be an interesting ride.