I've bit my nails all my life also =(
Used that stop'n'grow stuff - the taste is vile but after a while I got used to it and i bit my nails regardless of the taste!
I know about the germs and wash my hands often , even using that alco gel stuff but it would be better to just not bite my nails at all i suppose...
The only time that my nails were given a chance to grow was when i went skiing and i was wearing gloves most of them time and then i went and bite them off on the plane home! didn't even realise i was doing it =(
I agree that it's a disgusting habbit - i need some will power!