Yesterday Bing announced that specific links that have been 'liked' by your Facebook friends will be highlighted in the search results page. This is a development from the separate set of Facebook results that occasionally appear for generic search queries.
Although this feature is still being rolled out, a preview image on the Bing blog illustrates how displaying the Facebook 'Like' button may change visual indicators on a page and draw a user's attention to different parts of a search results page.
The implied concept is that the social web now influences where websites rank in search results. However, whilst this sounds like a gigantic revelation, it is not possible that this can influence anything but a minute fraction of all searches. Even Bing says that the algorithm didn't determine the 'liked' result to be most relevant to the query. In fact the display of 'liked' results operates more like an FYI, or footnote, to users.
"while our algorithms didn't feel it was relevant enough to make it the 'answer' we reference above, we are still able to indicate that my friend liked that link that happened to show up within the results."
So, whilst ostensibly there is space given on the first page to 'social indexes', social sharing does not actually affect the relevance algorithm. Put simply those URLs might be more relevant, but they are not by default.
Much like universal search on Google, which amalgamates video and images into its main results from separate data sources such as YouTube, social sharing factors seem to also operate as a separate data source.
You could say that these are simply an overlay of trust indicators that empower the user to have more confidence in Bing results.
Furthermore, as eye-tracking studies of Google's universal search have proven incorporating images, video, news and social circle results increase user attention and draw it down the page.
Therefore, for now, it seems more expedient for Bing to present 'social indexes' in the lower portion of search results pages (in a separate breakout section of results or area reserved for URLs that have been tagged by the Facebook 'Like' button), to generate 'stickier' and engaging search results.