The problem is that there isn’t a 1:1 correspondence between RSS downloads and readers, like there is for normal web pages (modulo caching and a few other issues). Bloglines is helpful enough to tell me that it has around 60 subscribers, and I know that I’ve served up around 24,000 RSS and Atom feeds so far this month, but I have no easy way to know if that’s 1,000 people with a slow refresh set or 11 people refreshing every 5 minutes, or even 50,000 people all reading via a portal. Plus, there are at least three “planet” sites syndicating one feed or another (PlanetRubyOnRails, PlanetTypo, and Planet Foo), and I have no clue how many readers they have, either via HTML or RSS.
I’ve been tempted to integrate a 1-pixel “web bug” into Typo’s RSS feeds more then once, but I don’t really like the privacy implications. Fortunately or unfortunately, I get the same effect any time I post an image here. The Flickr montage that I posted almost 8 hours ago has resulted in 347 image hits. Of those, 150 have no referrer, so they’re probably from standalone RSS readers, like NetNewsWire. Another 95 are from scottstuff.net, followed by 42 from Planet Ruby On Rails, then 24 from Bloglines, 16 from Planet Typo, 3 from Planet Foo, 3 from Google Reader, and a couple that are either comment spammers or internal feeds from stealth companies.
Does anyone have any good leads on how to track this sort of thing on a more regular basis? While we’re at it, does Feedburner just play session cookie games, or are they doing something clever? Finally, it seems clear that embedding images into RSS feeds works most of the time, but I’ve never heard of anyone using web bugs with RSS–did I just miss the discussion, or are people avoiding them?