I had several small things (laziness, poor libraries [in 2009], failing to get anyone else in the organisation even the slightest bit interested, my own lacking skills) but the overall worst problem was the feeling of the disconnect between the language and the host running my program. That is of course more or less always an issue when one uses a higher level language, but I felt Haskell was so far off that it disturbed me.
Also, the negative effect one gets after going back to one's own code after several months seemed much much worse in Haskell. Haskell code is too thick, too concise, not unlike mathematics. I find it ironic that the community, apparently, values that.
I bet others have had better experiences, but I definitely did not. Hanging around with Haskell clearly taught me many good things about program design, but I don't foresee myself wanting to ever write anything on the platform ever again.
