Facebook's Biggest Worry: Search Neutrality

The potential for social information reaches beyond search. Facebook's most popular feature is photo sharing and tagging friends in pictures. Picasa, Google's photo-sharing service, is not nearly as social. Ads also have the potential to be social, when people share and comment on them.

Neal Mohan, the Google vice president in charge of display ads, said that by 2015, three-quarters of display ads will be social. But Facebook already allows users to do this. Knowing the information people share on social networks -- like their age, gender and the restaurants and musicians they like -- could also help Google direct ads more effectively. Larry Yu, a Facebook spokesman, said his company expected competitors large and small to emerge but was focused on building a valuable service.

Privately, though, Facebook executives have said that their biggest worry is that Google will prioritize a Google profile page over a Facebook page in search results.