People say this a lot, but I honestly don't think it does. Code written using monads, whether the IO monad or a custom monad stack provided by a web framework, tends not to play too nicely with other Haskell code. It kind of demands everything be on its own terms and isn't as simple, clear, and transparent as the best Haskell code can be.

Don't get me wrong, I love Haskell, but I don't think it's very good at imperative programming, and I think there are much better solutions to be found to problems such as I/O.