I use SPDs for my commuting bike, and I have a pair of Shimano mtn shoes that I use (got them on sale too wich was a plus).

The shoes come with the cleat adapters not even in the shoes, so it's not even like you would have to remove something. Plus the mtn style shoes have tread, and while they aren't as stiff as road shoes, they are still pretty stiff. Plus you can walk in the without looking like a clown (a definate advantage).

I orginally had a pair of shoes that looked like regular sneakers, but you had to remove a portion of the sole to get the cleats in. If you never removed that section of sole, you would have never been able to tell they were bike specific, except for the fact that the sole was more rigid.