Just my 2 cents and some random thoughts here.
1) Report it. The owner has to take responsibility for his or her dog. I know that dogs can get out of the control of the owner, but when you have an agressiive hound you really need to be extra vigilant.
2) Buy pepper spray, less deadly but likely to make the point to the dog.
3) Why was your gun at home?
![rlol "rlol"](./images/smilies/rlol.gif)
Seriously, this could have been a mugger not a pitbull. As someone's tag line on here reads "Carry 24x7 or guess right"
4) I think I would have had to have been there to decide to shoot or not but my inclination would be to stand still, avoid eye contact and keep clam....but have my firearm out and ready and my phone out and dialing. I have seen the damge a dog attack can cause so I would definately draw the gun in readiness.