hi!
i posted this fun experiment in another post on washes & dish detergent,
but here it is again:
the soap breaks the water's surface tension as Matt said.
if you wat to see what this 'means', try this -
put some water in a glass, and sprinkle some black pepper on the water.
(it should float - that is the surface tension at work)
drag your fingertip across the top of the dish soap bottle
(i am assuming there is a blob of soap goo on yours too!)
touch your finger to the water's surface.
and there you have it!
the water is now 'too thin' to support the pepper flakes.