I like how it says "Rock-Solid Ecosystem", yet I have had the exact opposite experience trying to install even the most basic things with Cabal. I still can't get the Sublime text haskell plugin to work due to a dependency that fails to compile.
Also I found that installing stuff through Cabal was pretty slow. It's probably partly because Haskell libraries tend to be kept narrow in scope so it's necessary to install a lot of small packages to get a piece of functionality (take for instance the dependency list of Aeson, which seems to be the recommended choice for working with JSON : http://hackage.haskell.org/package/aeson ). Another reason is that Cabal compiles Haskell code into native code.