I use it to write Haskell. The syntax highlighting screws up the first line of multiline record declarations. Out of the box, it can't run a Hoogle search or launch GHCI like TextMate did. It's definitely not a fully-featured Haskell IDE, but it's a usable basic editor. Depending on what you're used to, it may or not be adequate. I switched because I liked the default color theme better (... I mean... because TextMate was being abandoned).