Google can do a much better job with consumer B than Facebook. Facebook has to guess based on his wall posts, listed interests, etc. Given the sad state of natural language parsing, how well do you think this will work? At best they'll look at the bands I like and recommend similar ones. If they're lucky, they'll end up as good at that as Pandora. Or Netflix for movies.

Google knows your interests based on what sites you visit. Perhaps you visit an auto blog, which has Google Ads. Then you visit MySpace, which has Google Ads. Google shows you auto ads on MySpace. This sort of thing is already commonplace with ad networks.

Google has your entire search history. This is a far more effective way to determine your interests than Facebook. Facebook can't get beyond what bands and books and movies you like right now.