Just my 2 cents worth...
I have worked in the bush from southern alberta, NWT and the arctic circle and everywhere between since I was 15. Working during the spring and fall when the bears are out and hungry. Ill say this. 2 people i worked with were killed by a black bear in 94/95? not exactly sure of the year. The company decided bear spray would be more then adequate to repel the bears we run across in the field which was almost always when working.
Since then Ive been in to many situations to count with black and brown bear due to our working locations, Ive seen cans malfunction, peoples fear grip them(understandedly so with a bear coming at you) making them drop the cans and also spraying way to early to effect the bear. Im not against the spray but personally would not count on it in a serious situation. It has obviously worked for many people on here, and I am definatley no expert on it.
It all comes down to the situation, I have walked over a crest to be 30 feet from a grizzy scaring the sh#& out of my self and the bear, i never would have had time to get a decent shot off if i wanted to. If it makes you feel better then bring it, every situation is different read up on reports of the spray you use and tests that have been done. if that was worth the 2 cents ...