What is Attention.XML?

On this weeks Gilmour Gang a discussion ensued regarding Attention.XML (a specification for tracking, prioritizing and sharing what people get from RSS). This could open the door for better management of the RSS fire hydrant. Would this allow for a 'killer app' in the aggregator space? I would imagine the need exists. RSS, Blogs, and Attention.XML (SYS-CON)(Printview)