I use the MTB style pedals as well. (Shimano SPDs) They have the clip-in on either side feature, and I use a sort of "casual" MTB shoe that I can walk in quite comfortably. For severe off-road use, I'd reccomend a tough, dedicated off-road shoe with the big toe spikes and all. You need some armor.

Don't worry about sneers from the dedicated roadies in their form-fitted shoes and aero pedals; 98% of riders will notice no difference.