Donald Stewart kindly took the time to analyze and document the download statistics for his xmonad package, a tiling window manager written in Haskell. His results prove that xmonad has been downloaded tens of thousands of times even though the project is not yet 3 years old.
Donald also notes that the number of source downloads dropped dramatically when xmonad became available prepackaged for all mainstream Linux distributions. This indicates that the Debian and Ubuntu popularity contest results (distros that cover over 70% of all Linux users) for xmonad should be accurate estimates for the current number of active xmonad users. According to those results, users are currently running around 180 registered copies of xmonad, making it the second most popular program ever written in Haskell!
Following the success of this analysis, Donald has announced his intention to automate this procedure in order to provide accurate download statistics for the thousands of Haskell packages currently available.