I used knee pads for a while, they help grip the bike some, but when you fall it is usually a direct hit and it still hurts... a lot. I still got bruises with knee pads, and they didn't even cover my whole knee area and lucky me, I would most likely get hit where the knee pad wasn't.
Since I got my asterisks, I haven't had a brusie, cut, or sore, on my knees. When I hit the ground the impact is spread througout the whole brace so that I don't feel anything hardly. I've fallen in some pretty tough stuff, and gotten up everytime thanks to my knee braces. I wouldn't trade them for anything. :)