One point not yet mentioned:
	Hands on the driver's shoulders are a definite no-no.  It feels
good for the passenger to stretch her arms, and a shoulder massage feels
good too, but the shoulders are connected to the arms, and the arms to
the handlebars...  Should you hit the brakes, the pressure on the shoulders
can make steering interesting.

Bundle her up if it's cold, make sure she has good gear (say it again),
an pat her thigh to let her know all is great.