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It seems to me that that would almost have to be part of the puzzle. If you read, which I know you have the SEL post on what social factors Bing and Google look at it touches on it if only peripherally. re: 3) Do you calculate whether a link should carry more weight depending on the person who tweets it? Bing: Yes. Google: Yes we do use this as a signal, especially in the “Top links” section [of Google Realtime Search]. Author authority is independent of PageRank, but it is currently only used in limited situations in ordinary web search. I can't help but think that the number and type of lists a person's Twitter account wouldn't be an obvious thing for them to include in their 'author rank'. Also the previous question hints at it as well: 2) Do you try to calculate the authority of someone who tweets that might be assigned to their Twitter page. Do you try to “know,” if you will, who they are? Bing: Yes. We do calculate the authority of someone who tweets. For known public figures or publishers, we do associate them with who they are. (For example, query for Danny Sullivan) Google: Yes we do compute and use author quality. We don’t know who anyone is in real life Also - if you think about it this could be symptomatically included as well. Because a person is included on more lists on specific topics (or not) they are likely to be more popular, which is likely to coincide a higher number of followers, RTs, etc. So maybe it's not directly related but it's a sign.

May I suggest this blog post from our friend Danny: http://www.seomoz.org/blog/how-do-tweets-influence-search-rankings-an-experiment-for-a-cause The take-a-way is yes, they do now, and probably will more so in the future so got on your social.