Joel Reymont has another post comparing Haskell development against Erlang.
He has recently rewritten the work he did in Haskell to develop poker bots for testing a poker server into Erlang:
Overall, I spent 10-11 weeks on the Haskell version of the project. The end result did not turn out as elegant as I wanted it to be and wasn't easy on the QA techs. They told me that the Erlang code was easier to understand and they preferred it. It took me less than 1 week to rewrite the app in Erlang. It's the end of that week and I'm already way past the state of the Haskell version. The Erlang code at 3900 LOC including examples and is about 1/2 of the Haskell code.
His post provides a great breakdown comparing developing between the two languages for this problem domain. Most of the issues seem to come down to lack of library support for concurrency and serialisation in Haskell, or the fact that those areas are not as heavily used in Haskell so have more problems.