As a followup on Brynn’s review of Delver, I’ve had an interesting exchange with Lachlan Hardy, where Lachlan expressed his disapproval of Delver’s crawling and unifying the social graph (content alone seems ok). My response is in this thread.
The important issue is that socially-connected search requires a comprehensive and unified social graph, which can be quite difficult to achieve. When users conduct their first search, they would expect all of their friends, friends of friends, and their respective content to be pre-indexed, for such a service to be of any use.
Skipping that part makes it impossible to bootstrap, and would be like a web search engine that includes only websites that opted-in to be included in the index, or like a FriendFeed version that shows no public profiles, and if you want to follow someone you must create their consolidated profile yourself. These can be regarded as far more privacy-observing services, but will probably never bootstrap as their real-life counterparts did. It’s all about keeping the balance right.