I just used it at work to build an ad server. For a web app that has a few well defined features, Snap is awesome and fast, and working in Haskell is totally a joy. It doesn't have the high level functionality that a web framework like rails or django has though. (yet)
Unfortunately, I used the old Snap extension API since the new snaplet API wasn't around when I started! So maybe if I have some time I'll refactor it to use the new API, which looks like it's a lot better than the old extension API.
One cool thing is if you statically link your binary and build on ubuntu 10.04, you can actually just directly deploy binaries to Heroku, even though it's not a supported language. Just throw in a package.json file or whatever to trick Heroku and specify your Snap binary in your Procfile.
Unfortunately, I used the old Snap extension API since the new snaplet API wasn't around when I started! So maybe if I have some time I'll refactor it to use the new API, which looks like it's a lot better than the old extension API.
One cool thing is if you statically link your binary and build on ubuntu 10.04, you can actually just directly deploy binaries to Heroku, even though it's not a supported language. Just throw in a package.json file or whatever to trick Heroku and specify your Snap binary in your Procfile.
THANKS SNAP GUYS!