This site will give you the lowdown on all things Big Cat: Cougar Information
From spending an hour reading the accounts, I'm impressed by: 1) how many cats were not starving, but merely looking for the next meal. 2) how many cats were unafraid of humans yelling, "getting big", waving sticks, etc. 3) how many cats were hunting/attacked at other times than dawn & dusk, including all hours of the night. 4) how there's no guarantee that a cat'll attack your dog rather than you, or even its supposed meal-of-choice--deer--instead of humans:
"There were 2 deer within 500 yards of him [the cat] and he chose us as his prey."--in the accounts, a tale of a 2-hour stalk, with a young fawn having been one of the deer.
Note: You might want to read the account of the two horseback riders who were chased by a cougar.