I've been partialy sprayed with pepper spray and it was the most uncomfortable feeling I've had. -In short I sprayed myself while spraying a dog in Romania, I got backspray due to the wind. It was rainy and I was wearing glasses and simply awefull. Luckily I got the dog enough that it took off, or I would have been helpless meat.

--So I wouldn't want to be sprayed with the dog stuff full on--

I've also had the "occassion" to spray:

-A Black bear. Kings Canyon NP
-The lead dog (?alpha male) of an attempted pack attack of Tibeten Mastiff's. Pack had 20+ dogs, lead dog took off after I sprayed it-pack veared off tempararily. Few Km out of Darchen Tibet.
-Couple other dogs.

I don't believe it will allways work (on animals or people), but its my first line defence if eggress isn't an option.

EDIT: adding, I carry my spray attached to my handlebar bag when cycling. I'd never have time to fumble about my bags or even pockets when I had needed it. Hiking I carry it in a cargo pocket in my shorts by itself. I had never thought of being charged with carrying a concealed weapon, so Stokell brings up a very good point above.