During the summer of 2011 I decided no more, and began to stop biting. I do not take credit for these ideas, I found them online when I decided once and for all that I would stop biting. So, as a person who made, admittedly, feeble attempts to stop biting I went about it in a strange way. Instead of the nail polishes that stop you biting, which you got used to if you bit enough, I followed advice I saw online. (Ha, I sound like one of those scam/virus ads)
It's super simple, pick one nail and say "I'm not biting this nail anymore". You can continue to bite the others, and just leave this one nail alone for a week. It's a small battle when the rest are bitten and there's one leftover, but a mild amount of willpower stops this. The next week you pick another nail which you will not bite, including the first nail you didn't bite and so on and so forth. This method works great as you wean yourself off your biting habit slowly and by the end of the second week you see the incentive of the first un-bitten nail that it'll encourage you to keep it up. The only qualm I had with this was the thought of how ridiculous/dangerous I would look with a series of random length nails. I counteracted this by lightly filing and shaping the first un-bitten nail after two weeks. It also occurred to me that my nails weren't going to appear much worse at random lengths than they did when they were bitten.
Now my nails are no longer the awful, bitten messes they used to be. I can paint them as much as I want, and they make my hands look better(?!). I'm not going to lie and say that I don't get tempted to bite them, I do a lot, especially when someone mentions nail-biting or one of them gets chipped. But after spending 12 weeks (I relapsed once or twice!) growing them out, and looking at how much they've improved now, I know better to leave them alone.
My only advice would be to stick to selecting one nail a week in combination with nails you've already stopped biting, and not taking on any more than that, or you'll more than likely end up biting the lot again. By the time you're down to five nails, you'll probably get antsy with being reduced to so little, so get a glass of water each time you want to bite.
This post probably sounds hilarious to people who don't bite their nails, but it's something of an addiction and is incredibly difficult to stop, most of the time you'll do it subconsciously.
Let me know how you get on!