After giving up on EclipseFP, I've worked a bit on haskell-ide-engine and leksah, contributing little things here and there to try to make the Haskell IDE ecosystem a little bit better. But at some point, I tried to update the GTK libraries on my Ubuntu machine to get leksah to run, and broke my whole desktop. Hours of fun followed to get back to a working system. So I thought again at my efforts last year to have a web based IDE for Haskell, because using the browser as the UI saves users a lot of pain, no UI libraries to install or update!
The functionality is fairly simple yet: there is a file browser on the left, and the editor (I'm using the ACE web editor) on the right. There is no save button, any change is automatically saved to disk (you use source version control, right?). On the server, there is a GHCi session for each cabal component in your project, and any change causes a reload, and you can see the errors/warnings in a menu and in the editor's annotations. You can build, run tests and benchmarks, and I've just added ":info" support. The fact that we're using GHCi makes it fast, but I'm sure there's loads of wrinkles to iron out still.
Anyway, if you're interested in a test ride, just clone from Github and get going!