RSS-publisher FeedBurner published an extensive report on RSS-readership and -usage, the latter meaning detailed stats on the number of indiviual item-clicks & -renderings (coined “audience engagement”). no big surprise - as mentioned before, Google Reader has taken the market of online feed-readers by storm…
as of yesterday, Google finally reports back RSS subscription-numbers to content-publishers, which basically means that feed-statistics like FeedBurner can now include the number of readers subscribed to a feed through Google Reader or the personalized Google homepage (this wasn’t possible before, meaning that probably thousands 
of readers wouldn’t show up in your feed-stats). in case you - like me - wonder how this works, Google simply embeds the number of current subscribers into the http-request fetching the feed:
User-Agent: Feedfetcher-Google; (+http://www.google.com/feedfetcher.html; 3980 subscribers; feed-id=1794595805790851116)
as a bonus they’ve also added an FAQ aimed at publishers.
btw, according to my own FeedBurner-stats, Google Reader’s marketshare among RSS-readers seems to rise:
a recent post on FeedBurner’s official blog explains some of the service’ inner workings on the basis of TechCrunch’s RSS-feed, which has been breaking the 100.000 subscribers mark a while ago. the article explains characteristics as subscribers and reach and gives insight on the diversified usage of newsreaders (in the case of TechCrunch, there are more than 500 applications out there!). it still doesn’t detail how online-readers like Bloglines or Rojo, proxying feeds for thousands of indiviual users, are taken into account. furthermore, the post announces integration of feed-statistics with classic log-based stats, provided by recently aquired Blogbeat, by the end of 2006.
