I've got platform on my cyclocross commuter, and clipless on my roadbike (speedplays, not SPD). I have no desire to put clipless on the commuter, but I do like them on the roadbike. The biggest advantage to clipless is that you can get very stiff soles on the shoes for more efficient power transfer, but if you go with the casual SPD shoes then that advantage goes away since the soles on those aren't so stiff (which makes them easier to walk in). I just use toe straps on the commuter - I can wear whatever shoes I want and the difference in speed is negligible, though the toe clips can be harder to get in and out of compared to the clipless.