A new feature shows a list of feeds from your site and the number of subscribers that come from Google services. "If your site publishes feeds of its content, this page will display the number of users who have subscribed to these feeds using Google products such as iGoogle, Google Reader, or Orkut. Because readers can use other sites and aggregators to subscribe to your content, your total number of subscribers from all sources may be higher." At the beginning of the year, Google started to include the number of subscribers in Feedfetcher's user-agent, but only people that had access to the logs or used a service like FeedBurner could see it. Now everyone who authenticates a site in Google Webmaster Tools can see the number of subscribers.
Even though this blog's main feeds are redirected to FeedBurner, they still have Google subscribers. That's because Blogger does a temporary redirect to FeedBurner (HTTP/1.x 302 Moved Temporarily) and Google Reader treats them as separate feeds.
Google Reader's main competitor, Bloglines, shows extensive information about each feed: the number of subscribers and a list of those who made their subscriptions public. This information is even included next to the feed's URL in search results and can be obtained through an API. The complete list of backlinks, displayed in Google Webmaster Tools, is publicly available at Yahoo: just use the link operator. So some of the data could be easily made available to the public without causing too much trouble.