I've only seen a griz charge once. I was bow hunting and it busted out of the trail ahead of me to chase something unseen on the other side of the trees. I have never been so amazed in my life to witness a creature so large move so fast.
To this day I think about the fact that I could not have reacted in time if I was the target. Hell...even if I had the spray in my hands and ready to go I don't think I could have done it.