Paul Boutin on why Bing may be a better search engine for most things (particularly if you use Facebook):
Beyond beating link spam, your friends’ preferences and recommendations may also provide a better guide to what you, as an individual, really want to find. If, for example, you’re shopping for a new pair of shoes, the most valuable search results may not be the most linked-to pages on the Internet but, rather, what your best friends want to be seen wearing.
It is an interesting dilemma that Google will need to deal with: unless you tie into Facebook/Twitter how do you provide results that are more relevant that page ranking? My guess is that Google would rather use tracking cookies and other methods of tracking user behavior — than they would tying you into a social graph that they don’t own.