Chameleons can be aggressive, and can bite.
I have a female Veiled, who is just over a year old, and is not very personable. She has bit me a few times, and has drawn blood. Some chameleons will tolerate ocassional handling, some will fight tooth and nail to stay as far away from human contact as possible. They are solitary animals, and don't get lonely or need company.
At this point it's really "luck of the draw" as to which catogory your animal will fall into. I have some that don't mind being held, some that I swear like to be held, and some that would like to eat my hand if I get to close.
You can take steps to lessen the chances of getting bit. I like to open the cage door and offer a treat before removing the animal. If done enough the animal will start to associate you and your hand entering the cage with a treat. They are not the brightest crayons in the box, but they do remember things.
Never reach over the top of an animal to pick them up, rather slide your hand beneath them and allow them to grip your hand, then gently left upwards to remove them. A prediator would attack them from the top, not the message we want to send.
In my opinion, and from my group, I feel that Panthers chameleons tolerate handling better then Veiled chameleons. They seam to be more relaxed in general.
-Jay