My bike is my only means of transportation (that is, the only one I use) and I just wear my SPD shoes everywhere. Wore them all winter in the snow, too, never bothered bringing a change of shoes with me. When I used straps I found that only specific shoes worked even remotely well anyway, the other ones would get hung up on the pedals or be too tall for the clips or get stuck in the straps, so I didn't see any reason NOT to buy special shoes just for cycling. Easier to get back into at stoplights, too, or if you clip out (for whatever reason) at high cadence on a fixed gear. Oh, and the cornering clearance and toe overlap are better and you don't have toe cages bouncing off everything when you wheel the bike around.

In short, clipless is F***in' sweet. Worst thing about the shoes is that they're hard to get into when caked with road salt.