One last infield fly question that has always puzzled me and hasn't
yet been addressed.  I believe the rule also does *not* deal with this
situation:

If Infield Fly is declared and the ball is caught, runners can tag up
and advance at their own risk, as on any fly ball.

However, if the Infield Fly is *not* caught, at what point can a
runner legally leave his base w/o fear of being doubled off for
advancing too early?  When the
ball hits the ground?  When a fielder first touches the ball after it
hits the ground?

Enlightenment would be appreciated.