The comments about yelling and making yourself look as big as possible sound right on - since dogs would seldom hear humans howling and carrying on like that, I imagine it would have significant shock effect.
SPEED is a big factor here as well - not only running, but also fighting. At least from my point of view, I have been absolutely amazed at how quickly dogs can fight / bite. I saw a dog fight once, between one 'bad boy' stray and four others. The 'bad boy' started it, and the four tried to finish it. The 'bad boy' got on his hind legs, put his back against a parked motorcycle, and took care of business - in about 5 - 10 seconds. All I could see was a blur of teeth and blood. The 'bad boy' won.
Unless I'm well armed and ready, I'll still climb the tree or otherwise escape. I'm sure a decent human can take one dog, but up against two attack dogs - that would be a real accomplishment. And, as I think Rob mentioned, perhaps an experience you'd have to relate to the other severely handicapped people in your hospital ward!
Let me ask another question, mentioned above in passing - stare or not stare? I was taught years ago to walk away from the dog, don't show fear, but keep the dog in your peripheral vision until you're out of its territory. I was taught that staring at the dog actually increased the chance of an attack. What do you all think?