We have a 22,000 square foot facility with 24 foot ceilings.  Our
overhead lighting is mecury vapor lamps.  We have suspended tracks which
get power from the ceiling.  From them, we use spots and also attach our
floor exhibits to the tracks for power.  This system provides additional
needed flexibility since the floor power plates are always in the wrong
place.  I have seen the power cords going up from exhibits at many
museums and feel it is a good way to deal with the problem.  As a
children's museum, we really don't like cords on the floor and power up
solves that well.  The drawback
is that you can't hang banners from the tracks.  Our banners are ceiling
suspended.