I have almost totally forgotten how to ride without being clipped in. Personally, I hate the feeling of my feet flying off of the pedals. I might ride to the pond (1 mile) in my regular Keens, but, it's just as easy to wearing my cycling sandals.
I don't ride in the city, but I do do errands sometimes on my Coda, that necessitates a lot of stopping and starting. While this bike has campus pedals, I rarely use the flat side. One time I did a 4 mile ride into town in regular shoes, was stopped at a light, and I could not get started without being clipped in. It was like I had forgot the whole motion I learned when I learned to ride as a kid. After that little experience, I never wore regular shoes again.