the only problem is the people who are using their tumble type skills can't run with the keys... so therefore it creates some problems.
i don't run, but some people rely on their tumble skills and spring attack type feats and skills.. so it would just have a conflict for some players..
otherwise, i think it's a GREAT idea. it would be a whole lot better than quickbarring all your feats and then having more that you have to put on the Shift or Ctrl quickbars...