Ian Witten's lecture last week commented that web search, like Google, was akin to asking an oracle to give you an opinion on what the best web pages were that would satisfy your query. Most users are not aware of how Google ranks pages (we assume its benign and to our benefit) and must therefore trust Google's rankings. Ian argued that what we would often prefer is to get search results from trusted friends or colleagues. This is called crowd sourcing or social search.
Facebook is moving in this direction with its "Like" button that is now appearing all over the web. The idea is that over time we'll start to use Facebook to satisfy web searches based on what our social network has expressed as their "likes". It will be interesting to see how this pans out over the next few years.