Carbon Fiber is too brittle for street use and carries the risk of catastrophic failure that you wouldn't experience with a metal rim. If it ain't for track-use-only I would say stick with Magnesium or the stockers.
~ Blue Jays ~
In all my years (not as many as Dad or Smitty, but quite a few) I've never seen or heard of a CF rim suffering a "catastrophic failure." Maybe I just don't get out enough, but am I the only one that hasn't seen and/or heard of this happening?