The problem, in this case, is that the link urges users to come try out Google’s flashy new social network, which competes directly with Facebook, leading to speculation that Facebook would somehow be hiding these links intentionally.
What is, perhaps, surprising is that some of the finger-pointing on this is coming from Google, which itself uses similar filtering technology on its own search results.
http://news.cnet.com/8301-1023_3-20093213-93/google-facebook-spar-over-google-invite-issue/
