My dodgy understanding of reverse swing was that the fielding team work the shiny side of the ball by putting as much moisture on the shiny side as they can. At a certian point (about 40 overs) the shiny(moist) side of the ball has extra weight in it than the rough side. The rough side of the ball will travel through the air faster as it is lighter and the ball will reverse swing.
Reverse swing also works better when it is overcast. Not so good in Australia
