There is a Haskell-written OS! Can't wait to play with this...
House - http://programatica.cs.pdx.edu/House/
Another interesting angle are Linux LKMs in Haskell. This is pretty proof-of-concept... If I ever have time I'll see if I can play with this. Hmmm. I wonder if with new version of GHC this isn't limited to IA-32 anymore.