Phil Shoemaker has a lot of up close and personal experience with big Alaskan bears and he's comfortable with a .357 and the right bullets. He has a great article in the June 2003 Handloader titled "Handguns and Bears" on the subject.
The formost virtue of a handgun is that they are portable and likely to be with you at all times. Any handgun beats no gun and a determined person with one should be able to survive most situations. My choice is usually my S&W 44 Mtn Gun as it is comfortable and familiar. I also occationally carry a S&W M-13 357 with hard cast 200gr Fn bullets. i wouldn't feel unarmed with a Glock, Ruger or other good auto but as we used to say in the military - the purpose of a handgun is to fight your way to a rifle.
My take - a handgun you can shoot well, including a .45acp, with the right bullets is a hell of a lot better than a cannon you can't shoot, a sharp stick, or a rifle you left in the truck because it was too heavy to carry.
