MTB shoes are good and can be great for walking, etc, but keep in mind that if you get a shoe with a flexible sole and no cinched in heel cup you're missing the boat.

To really get the benefits of clipless riding you need a shoe that has a totally stiff sole, cups your heel and has a strap system that tightens against your toes (for pulling up) and holds the shoe tight to your heel. Look at the Sidi racing shoes for what I mean. Lace up MTB shoes with flexi soles are not going to give you as efficient torque transfer or the 'i'm connected to my bike' feeling that a racing shoe will give you.

Don't discount what you get from the non-MTB style pedal/shoe systems.