I have one veiled right now, he's all that's left from little breeding eperiment (sold the rest, gave some away).
His mother bit me, and yes, it did hurt. She tore in there pretty good, drew blood, etc...
That's the only time I've ever been bit by a chameleon. I've been bit by many other reptiles though, most were small ones that I let bite me, but there were a few (like the 7 foot reticulated python) that caught me by surprise.
Surprisingly, though the retic drew a lot more blood, it hurt a lot less than the chameleon bite. Probably because they just bite and withdraw, whereas the veiled bit in a tore.
Not to scare you, I still hold my chameleon, and held his mother too. They freak out when you are reaching for them, but once you get them on your hand, they tend to calm down. Well, most do.