I guess my point is that, talking generally now rather than about any one specific site, we just don't need to put as much weight as perhaps we used to on what Google think of our pages this week. More and more of our traffic comes from personal mentions, passed on by people who are actually interested in what we have to their friends with similar interests, and people who find us that way are far more likely to be genuinely interested themselves and to enjoy our material, increase our income, or otherwise match whatever we created the site for.
People use buzzwords like "going viral", but really this is just the same old exponential growth of word-of-mouth recommendations for good products, speeded up thanks to modern communication technologies and the social networks they support.
Obviously we still make our sites accessible to search engines. It's not like it's difficult to do that if you've got real content and a sensible information architecture, and after all, a bit of extra traffic never hurt anyone. Maybe, if an enthusiastic person finds us that way, it could even seed a new network of people finding us.
But I see this becoming less and less of a priority and dedicated search engines becoming less and less relevant for a lot of sites as people learn to use social networks to spread the word. In particular, I don't see cbeach's original idea of a "search engine that ranks mainly on social-graph recommendation" adding much value in that scenario, simply because the social networks will probably offer similar functionality without needing a third party anyway.