Google Reader reveals number of subscribers

Google now shows you the number of Google Reader subscribers to your RSS feed. They do that by adding a value to the HTTP user agent field when fetching your feed. You can find the number in your raw logs - it looks something like this:

72.14.199.72 - - [16/Feb/2007:08:44:34 -0600] "GET /feed/ HTTP/1.1" 304 0 "-" "Feedfetcher-Google; (+http://www.google.com/feedfetcher.html; 7 subscribers; feed-id=5769402134728990362)"