[Haskell-cafe] Disadvantages of de Bruijn indicies?

Hi, de Bruijn indicies look quite nice, and seem to eliminate a lot of complexity when dealing with free variables: http://en.wikipedia.org/wiki/De_Bruijn_index So I was wondering, are they suitable for use in a compiler? If so, what are their disadvantages/advantages? Is there any particular reason that GHC (as an example) doesn't use them in its Core? I'm trying to decide if I should use them in my compilers data type - and would like some recommendations before I start. Thanks Neil