We do once a week too.  I take him to the groomer every 4 weeks (I keep him very short) and do nails and trim his pads and face after each bath.  I use Cloud Star shampoo & conditioner.  We LOVE IT.  It's lavender scented and does not dry out his skin at all.  He is so fluffy after a bath.  People who tell you to bathe less than every 2 weeks must not have Yorkies! 
