This doesn't hold account of people installing it through packages or compiling from the github repositories or downloading the flat file without a torrent.
Understood. I suspect flat file is #1 (although it's a big file and the erlang.org server isn't on the world's fastest pipe). I doubt too many "active users" use distro packages because of how out of date they often are. But to me, just for an order of magnitude estimate, it suggests an active Erlang community of perhaps a few thousand users. Just helps me put a number on it when I had no reference previously. You probably have your own estimates based on your traffic stats... and thanks for your Learn You Some Erlang tutorial: http://learnyousomeerlang.com/ !
Yeah, Learn You Some Erlang gets an average of 4800 unique visitors (or 41500 page views) a month according to awstats.
There are about 100 (mostly idling) users in the #erlang channel on freenode and a few hundreds on the mailing lists. There are 1,800 subscribers to r/erlang on reddit. You have 719 watchers of the Erlang/OTP project just on github. Trapexit's project tracker has a bit more than 1450 projects (http://projects.trapexit.org/web/) there.
Note that it's been a few versions since Ubuntu started shipping with a minimal version of Erlang to allow CouchDB to be used there, so the repository stats likely show a whole damn lot of users, so it'd be hard to count how many developers you have precisely.
A few thousand developers might be a good estimate, although those would only be the vocal, active ones.
