I used to (as in, until last September or October) bite my nails constantly out of a compulsive grooming habit that left the poor things as stubs — it definitely wasn't an anxiety or boredom issue, considering I'd be playing Battlefield and chew my nails still, and I'm currently going through a very nervous part of my life. After that I'd just chew away at the cuticles until I couldn't use my fingers due to the pain. I hid my hands whenever I had the chance, too; try to keep people from seeing them.
But I've almost entirely stopped, and the actual biting is miniscule — I manage to catch myself and stop without a problem, though I can't help but feel the urge whenever I don't have a nail file on hand. I started painting my nails, grew them out enough to file them into a smooth curve, and now they're all nice and pretty. (Really long, too.)