Of course, there are bears, and then there are BEARS. Black bears are relatively small and not usually aggressive. Browns get much larger, and while opportunistic feeders, are also huge, capable predators. Special care should be taken to avoid bears in the late Fall or early Spring -- they're either trying to fatten up for the Winter or are just coming out of hibernation and very hungry. If you get between a sow grizzly and her young cubs, you're dead meat -- many mountain men perished as the result of that kind of encounter.

I've read that the best bear defense strategy is to be aware of signs that you're in bear territory and simply make noise so that you don't surprise one. As a general rule, bears would rather avoid people and will usually move along unless they feel threatened. Black bears would rather scavenge a carcass than try to take human-sized prey, but I wouldn't want to depend on that with big browns. If you do encounter a bear at close range, I've heard that the best thing to do is calmly back away -- don't run. I've also read that they'll scare if you yell and act aggressively, but in my (admittedly inexperienced) opinion, that doesn't leave you with a good fall back position if they decide to take you up on the challenge.

I spoke with one Korean-war era army vet who claimed to have checked out a BAR to go bear hunting -- I'd be confident even against even a charging griz with a full-auto .30-06, but that's about what I figure it would take. Anybody who has no choice but to go head-to-head with a bear using a knife will take damage and be lucky not to bleed out even if they "win".