It's very important to me. I have a veritable arsenal of old games (roughly 30-40 games per system with the exception of the NES which is around 50-60).
I love all my old games. Even today I can still enjoy a game of Star Tropics 2: Zoda's Revenge (NES) or Vectorman (Genesis). Backwards compatibility is one of the most awesome features developed in the last few generations and I really want it to continue.