That's an interesting analogy but flawed because getting traction for a better search engine does not depend on network effects nearly as much as it does for a better social network.
If none of my friends use Google, it's still as valuable to me. If none of my friends use Facebook,...
Sure, network effect is a big deal for sites like facebook, but it's not everything. Network effect didn't save myspace. If something much better than facebook came out people would start switching to it, and quite rapidly the network effect bonus would vanish. My point is that there is every reason to believe that the possibility there could be a social networking site significantly better than facebook is very high. Precisely because the problems in play are incredibly hard problems and nobody has solved them very well yet.
If none of my friends use Google, it's still as valuable to me. If none of my friends use Facebook,...