@JoshRoss:

I have ... I don't do as much as I like but I have slowly been working through ProjectEuler problems.  I usually do the problem in C# with LINQ and Rx, and then in Haskell, or sometimes the other way. 

The installer, cabal and everything work really well ... I use Notepad++ for editing but I've tried Leksah an IDE for Haskell, and it seems good so far but I haven't built anything non-trivial, in terms of project size/complexity, so I don't know how it will fare for more serious work.

Disclaimer:  I am still learning to read complex Haskell - the actual libraries with optimizations are almost always more complicated in practice, vs. what you may see in tutorials.  Other than pre-STL C/C++, I am not aware of bigger gap between theory and practice when it comes to optimization, but maybe that's just me because of my lack of experience.  Other than that, Haskell is awesome.  If I had a chance I would use it for my "real work", I would.