Google announced their new feed reader at the Web 2.0 conference.
Sadly, reaction to the new service have been negative, at least in part due to Google's failure to build the service to perform quickly with the sudden influx of demand.
What I find most interesting about the service is that the unusual default view in the reader is to show recent posts from all of your feeds ordered by "relevance". According to the Google Reader FAQ, this ordering of the articles "prioritizes the items that seem most relevant to you."
More details are lacking. Jeff Clavier seems to have additional information and says, "The relevance is based on an analysis of your blogroll, and surfaces posts that relate to your areas of interest (this is reportedly work in progress)."
Very interesting and surprisingly similar to what Findory recently launched. Findory's feed reader is unusual in that the default view shows top stories from your feeds ordered by recency and relevance.
Findory's definition of "relevance" is based on what you have read in the past. How does Google's feed reader determines relevance?
Offhand, I would guess that it is simply the same relevance used for Google's blog search. That is, it favors recent articles from authoritative and reputable weblogs. I don't think individual reading behavior influences relevance yet, though I wouldn't be surprised if they later decided to favor feeds you read recently.
I very much doubt that Google uses the detailed data about what articles you have read for relevance like Findory does, but perhaps Google will move in that direction someday.