Seems like several people are asking about this and I've seen the common
answers about biting being motivated by fear (due to prior maltreatment),
frustration (I want to get down now!) or desire for attention (I need a
treat now!).
 
I'm pretty sure I've got one that is into biting as a sign of affection.
She's about 3 years old and was always a biter due to prior maltreament
before she was rescued.  Anyway, we don't believe in the "flick the lower
jaw" approach so she was never discipled physically but was just frequently
handled.  Within a year she settled down to a very friendly little thing
with a tendancy to nip if you were near the treats cupboard (attention
getting).  She plays rough with the others and if you start a rough house
with her she will respond appropriately.  However, recently she has taken to
climbing up onto you when you are in the chair and settling in.  Shortly
afterwards she starts nuzzling the hand or wrist.  This is usually followed
by a short period of licking and then the chomp; head twisting if she's got
real good hold.  Strange thing is she doesn't show any sign to want to rough
house if you try to respond that way.  (I usually roll her onto her back and
vigoursly rub her belly to get her worked up for a rough house.) She's much
more content to just stay put and nuzzle and periodically chomp.
[Posted in FML issue 1784]