This is why I ride with dynamite lining the tubes of my bike. You have 30 seconds to deactivate it once I'm off the saddle. If I go down I'm taking those 'lil bastards with me.
With that being said, I know a fellow commuter here that carries a can of Mace where she can quickly access it. She says she's had a few close calls where she thought she might need it. Mostly from fat angry motorists.
Being a dude, in Boise ID, I'm not to concerned. I've never been threatened on the MUP or the Streets, but I don't ride through shady areas either. The closest I've come to being in a fight with a punk was on the MUP - this guy on what looked like a large BMX or smaller mtn bike was hopping around, doing 360's on his back wheel. His buddies heard my loud "PASSING LEFT", and he started going in a straight line again, so I thought I was good. Little do I know right as I start to pass him and he launches into another 360, I swerved away and his front wheel came about 8 inches from my face. I put the hammer down and left them in the dust after that.