Belle:

Actually its like a 5 hour flight if you go direct from JFK (not via the concorde), so shaving a couple hours off might be worth it.

I know that BA used to fly the concorde between Bridgetown Barbados and LHR. Saw it when I was down there a few years ago. LHR to Barbados on the concorde might be worth it as on a 747 its a 10-12 hour flight I believe.