Twitter is rolling out advanced photo search capabilities. The idea is to create a richer search experience within the social networking site itself so users aren't tempted to go elsewhere to find what they are looking for.
Google's updated its social search algorithm to give more prominence to results from a user's friends.
Microsoft's made a major upgrade to Bing, adding much more integration with Facebook, in a move that could perhaps see it taking on Google properly for the first time.
Google has bought Aardvark, a social search company which allows you to badger complete strangers with stupid questions at the touch of a button.