I've been bitten by a 10 inch Stars and Stripes. If it wasn't for my fingernail I would probobly be missing the very tip of my finger. Very deep wound, not really painfull as the teeth must be scalpel sharp. It took a bit but got it closed with super glue.
Ive been bit my my MBU before. Left my fingers above the tank and he thought it was a worm. My guys teeth are well worn so it didnt slice through my finger, but it did draw a little bit of blood. He smashed it pretty hard though. I make sure to be aware of were I leave my hand when cleaning the tank from now on.