I've been a nail-biter my whole life. I wore false nails for to break the habit, and it took nearly 2 years. I haven't worn false nails or bitten my real ones for 6 months now, so it was worth all the money and time sat in the salon (although it was a pain at the time!). Now I just chew at my cuticles instead......GOOD LUCK!
I've never bit my nails (well I have but only when their chipped or something), an I can't actually think of a bad habit I've got at the moment although I'm sure there are plenty. I'm sure someone will point them out to me.