By far they are a bigger problem than cages in Philly. I usually yell "Bike!" at them. Then try to come as close as possible to hitting them without actually doing it. Old ladies and pregnant women are of course excepted from the latter. I think they expect that you are able to stop faster than cars (not true) from the same speed.
Plus, Sheldon has taken care of this:
http://www.sheldonbrown.com/lirpa.html#bayonetz