How many subscribers does your feed have?

Google Reader added a subscriber reporting feature for feed publishers today -- though it is worth noting that Bloglines has been doing this for years already.  As a publisher, it can be very difficult to get a sense of your actual readership due to the vast number of people using feed aggregators -- that's why this feature is so important.
You can read more about this new addition, and at the same time get some good publisher tips here.  Below are typical User-Agent headers for Google's Feed Fetcher and the Bloglines equivalent:

User-Agent: Feedfetcher-Google; (+http://www.google.com/feedfetcher.html; 4 subscribers; feed-id=1794595805790851116)
User-Agent: Bloglines/3.0-rho (http://www.bloglines.com; 4 subscribers)