Crab, slips, and crossed controls

Hey,

Some of you may have heard of Air Canada 143 [http://www.youtube.com/
watch?v=dfJIpA2gv1g] which ran out of fuel in mid air and had to make
an emergency descent at velocities way above the normal limits. The
pilot's makeshift technique was to engage a sideslip to decelerate the
aircraft (which by then had no flaps, and only minimal hydraulics).

Now I thought that sideslips (and crabs--whatever the difference
between the two is...) were only to be used to handle crosswinds. I
didn't read anywhere that they could be used to bleed excessive speed,
although it makes sense from an aerodynamics perspective. Anyone out
there used sideslips for anything other than crosswind approaches?

PS: I have read about many cases of jetliners that had to make
emergency descents at abnormally high speeds, but the AC143 seems the
only one to have used the sideslip.