Biking in the City

I will (hopefully) be moving to center city philadelphia this month, and if anyone knows Philadelphia or any city for that matter, having a car is really a bad thing, but good if you have a brand new beautiful bike. I haven't had the best luck clipping in and out of my pedals (I fall at least twice on every 2 hour ride I've ever done) but my nerves are kind of crazy as far as biking in the city. Sure falling on a back street isn't to bad (there are less cars to get hit by and people to laugh at you) but in the city I could careless if someone laughs at me, my whole thing is not falling in the middle of Market Street and getting run over by a bus.

Does anyone (city bikers, or suburb bikers) have any advice on how to unclip spontaneously? Its very hard to have any warning when crossing a busy street in the city with the way the traffic lights turn so fast, I can only imagine how it would be on a bike.