I'm using Arch now for two reasons. It is surprisingly easy to install and maintain. The documentation and wiki are the real reason behind this. I guess that's the surprise: docs beat guis, at least in linux distros.
Also I can keep a bleeding edge system up to date with out much trouble. I never could figure out how to do this with unbuntu.
I guess there is also a third reason. Arch seems to keep up with haskell developments very well.
I consider myself to be an underzealot. I wouldn't recommend it to anyone who doesn't already know how to get in and out of nano or vi.
My main motivation came from noticing the extensive support for haskell packages. I would have been happy to use a debian-based distro, but haskell seems to be too bleeding edge for distros like ubuntu to keep up.
Also I can keep a bleeding edge system up to date with out much trouble. I never could figure out how to do this with unbuntu.
I guess there is also a third reason. Arch seems to keep up with haskell developments very well.