I am glad someone posted about the running downhill myth. That is totally not true. Bears are way more agile than humans, too. Running is a bad idea in general. Unless you are Adrian Peterson, I really doubt that you can juke and side step a swipe from one of those paws. Even a small black bear is strong enough to annihilate a human. There are lots of sites for bear encounters and tips and running is consistently a no-no. If you have seen one of those dudes skinned out, they look like a young Arnold Schwarzenegger with wolverine claws.
http://dnr.alaska.gov/parks/units/kodiak/kodbears.htm This one mentions black bears, too.
The national parks rangers tend to teach that guns, in particular handguns, are not effective against charging bears. Prevention is the best medicine in this case like most other things. Like someone else said, unless there are powder burns, self defense is going to a tough sell. I am just saying that if you are going to use the shotgun for bear defense, make sure you have your ducks in a row. It should be the last line of defense, in my opinion anyway.