According to the Official Google Reader Blog Google feed crawler, Feedfetcher, started to report subscriber counts. "The count includes subscribers from Google Reader and the Google Personalized Homepage, and in the future may include other Google products that support feeds."
What I found it interesting is that they do it via User Agent string. That's a very simple and nice solution and it's apparently not something new as I just looked at my blog log file and found subscribers info from a variety of feed crawlers:
GET /blog/index.xml - x.x.x.x HTTP/1.1 Bloglines/3.1+(http://www.bloglines.com;+154+subscribers) GET /blog/index.xml - x.x.x.x HTTP/1.1 NewsGatorOnline/2.0+(http://www.newsgator.com;+99+subscribers) GET /blog/index.xml - x.x.x.x HTTP/1.1 Feedfetcher-Google;+(+http://www.google.com/feedfetcher.html; +167+subscribers;+feed-id=xxxxxxx) GET /blog/index.xml - x.x.x.x HTTP/1.1 Newshutch/1.0+(http://newshutch.com;+12+subscribers)
And even such funny user agent as
GET /blog/index.xml - x.x.x.x HTTP/1.1 Mozilla/5.0+(X11;+U;+Linux+i686;+en-US;+rv:1.2.1; +Rojo+1.0;+http://www.rojo.com/corporate/help/agg/; +Aggregating+on+behalf+of+15+subscriber(s)+online+at+http://www.rojo.com/?feed-id=xxx)+Gecko/20021130
One might claim that's user agent header abuse, but I don't think so. Here is what RFC 2616 (HTTP) has to say:
14.43 User-AgentThe User-Agent request-header field contains information about the user agent originating the request. This is for statistical purposes, the tracing of protocol violations, and automated recognition of user agents for the sake of tailoring responses to avoid particular user agent limitations. User agents SHOULD include this field with requests. The field can contain multiple product tokens (section 3.8) and comments identifying the agent and any subproducts which form a significant part of the user agent. By convention, the product tokens are listed in order of their significance for identifying the application.
Statistical purposes that's it.
Oh, and while at it I should admit I hooked up to the Google Reader completely and haven't run RSS Bandit for months now. RSS Bandit has tons of cool features, but I always knew I need lightweight Web based feed reader. I tried Bloglines repeatedly, but only with Google Reader I found myself really comfortable from the first minute. That's great application.