I am in the same boat. Although I'm looking at a completely clipless setup. Time ATAC's are a clipless system made for mountain bikes and are very popular amongst the fixed gear crowd, as well as Crank Brothers' Eggbeaters. I believe both can be worn with mountain-bike shoes were cleats are recessed, therefore easier to walk on.

If you want a dual clipless and clipped system, I believe Shimano makes one of those. One side is a platform pedal while the other side has cleats. Sorry I dont know the exact model though.

I'm pretty sure somebody with more experience would share their thoughts on this.

Goodluck!