You wont be able to see who gave you postive or negative props. Check out the thread though and you can visit the link that will tell you what post has the most and who had the most.....and stuff like that.
You can give and receive them for whatever you want to. But with that ability you should really be giving them for helpful posts. Like Taylor's last post. It was helpful and got you the answer so you could give him a prop. Also you can disable them if you do not want to participate.