I have an almost three year old Quaker who likes to bite a lot. I have read the Parrot Training articles and none of the reasons for biting seem to fit. She is very protective over her cage and her toys (understood), she gets a lot of attention and time outside the cage. The only time she is in it is when I leave the house or when it's time for bed.
Sometimes when I sit at the table she will come walking over "ever so sweetly", step up on my arm and take a chomp. I have many cuts and bruises to show for it. I squeak in a high pitched voice to let her know it hurts and I put her back on her cage. She loves to be cradled in my hand and petted and is otherwise a very good pet, but I can't figure out why she will purposely walk over to me looking so sweet like she wants some petting and then grab a hold of my skin and either tear it open or leave a bruise.