http://www.boingboing.net/2007/01/31/powder_turns_bathwat.html
The first thing that comes to mind is having a Ghostbusters themed party.
The next is, with the water absorption rate being so high, how long until someone desides to make a mixed drink with the stuff and dies of dehydration?
And the last thought is, I wonder if there is a safe liquid you could suspend the powder in, and make a double barrel/chamber squirt gun to slime people with.