Liam Morrison thinks Google might be using RSS Subscribers to a blog's feed as a ranking algorithm, if they're subscribing via Google Reader, iGoogle or Google Webmaster tools - then Google will keep track of it- he calls it Google AttentionRank.

"..If your site publishes feeds and you are signed up to Google Webmaster Tools, Google is now showing data on the number of subscribers to your feeds via Google products such as Google Reader and iGoogle. "

It would kinda make sense, but I'm not sure they're doing that yet.   If that's so, then a blog that has a lot of RSS Subscribers, all things being equal, should do better in rankings than one that has less.

At this point, we'd need to blogs of equivalent number of backlinks, both writing more or less, the same content, and one having substation ally more RSS Subscribers.  It would be hard to tell since there's so many other factors that could influence the results.