I would like to strive to find objective data on the use of extensions. I started a table here which summarizes how popular extensions are in real-life code. We need more data points, though. http://hackage.haskell.org/trac/haskell-prime/wiki/ExtensionsExperiment I have a short program which queries the hackage database, gets some details about all of the packages there, and summarizes them into a table. Right now, there really aren't that many packages on HackageDB, but hopefully more will appear. HackageDB is here: http://hackage.haskell.org/ModHackage/Hackage.hs?action=home You can upload packages with Cabal-Put, but it's pretty hackish right now. I put detailed installation instructions on the wiki: http://hackage.haskell.org/trac/hackage/wiki/CabalPut A list of cabal packages that might be good for uploading is here: http://hackage.haskell.org/trac/hackage/wiki/CabalPackages The more packages we get into HackageDB, the more accurate objective data we can build. Let me know if you want to help! peace, isaac