Subscriber info is now included in the header left by Google’s Feedfetcher spider when it grabs a feed. This information tells publishers how many of its users are subscribed to their feeds.
A look at the header left by the Feedfetcher spider provides information about the total number of users subscribed to that feed in Google Reader and the Google Personalized Homepage.
Initial analysis seems to indicate that Google reader might be the leading platform currently in use to view RSS feeds.
