I find that the Haskell language is too vast to be directly useful to me. It appeals to my programming language fetish, which is a curse when I want to get something done. I rapidly end up devising between different ways of laying my types down, which is brain-gasmic, instead of how to get a result. And in the end I find out that it's not efficient enough and that I have to re-write the program with less "pureness" to get some juice out of it.

In contrast, OCaml's syntax and model is quite simple. The IO is not pure but at least I don't have to choose between 20 different ways to do it. There is not as much activity in the community but at least you don't get distracted by the latest monad library. For somebody who just want to crunch numbers, I think it is a good choice.