Followed the instructions over here: http://git-annex.branchable.com/forum/git-annex_on_OSX/

and had to install the following extra packages to be able to get make to start:

[realizes pcre-light is needed but pcre not installed on my mac]
sudo port install pcre
sudo cabal install pcre-light

But then I got the following error:

ghc -O2 -Wall --make git-annex
[ 7 of 52] Compiling BackendTypes     ( BackendTypes.hs, BackendTypes.o 

BackendTypes.hs:71:17:
    No instance for (Arbitrary Char)
      arising from a use of `arbitrary' at BackendTypes.hs:71:17-25
    Possible fix: add an instance declaration for (Arbitrary Char)
    In a stmt of a 'do' expression: backendname <- arbitrary
    In the expression:
        do backendname <- arbitrary
           keyname <- arbitrary
             return $ Key (backendname, keyname)
    In the definition of `arbitrary':
        arbitrary = do backendname <- arbitrary
                       keyname <- arbitrary
                         return $ Key (backendname, keyname)
make: *** [git-annex] Error 1

My knowledge of Haskell (had to lookup the spelling...) is more than rudimentary so any help would be appreciated.