This is probably not as fun as the stuff Carmack is up to, but if anyone out there wants to see some examples of "real" stuff done in Haskell (for "typical startup" values of "real"), check out Real World Haskell. I found it to be a great read, especially after working through Learn You a Haskell.

http://book.realworldhaskell.org/read/

He tweets about his experiments in various languages quite a bit if you don't already follow him there.

https://twitter.com/ID_AA_Carmack