I use SPDs for NYC traffic, and don't have any problems -- or at least I haven't been run over by a bus yet. Three thoughts:

1. You don't always have to be clipped in just because you have clipless. The pedals will still spin just fine. I wouldn't do it for long distances, because it's annoying, but you can ride in bike shoes on clipless pedals without being in the clips. That means that if you've got a stretch where you'd rather not be tied in to the bike...unclip for a while.

2. For short distances, SPDs work fine with regular shoes. It's not entirely comfortable, and anything more than 2 or 3 miles I wouldn't do it. But over that distance it's not going to bother you too much.

3. If you go with SPDs, get the multi-directional clips (so that your foot will pop out regardless of which way you twist it), and set the tension all the way down. You don't need it tight for city riding, and if you ever start to fall you'll probably find yourself popping right out.