> I am sure that the Debian people must have stats of how many updates they see per day, and it would not be too hard to finger-print them, but I think nobody does.
I don't believe Debian could say how many downloads there are. Debian is distributed by a network of FTP/HTTP mirror servers, most of them outside any control by Debian. http://www.debian.org/mirror/list shows 50 primary and 400 secondary mirrors.
But some people don't even use them. E.g. if one has a root server at a hoster such as Strato, they use by default their own mirror server to save on traffic. In my company we produce an embedded product that runs Debian and of course the installation is done using our own partial mirror. Setting up a Debian mirror is so easy (much easier than it was for me to install CM on my phone) that one can assume that there are many thousands of them in universaties, companies and even private households.