A great article on setting up your delay to work correctly.
http://www.artemismusic.com/page.php?id=92
One thing about Riffworks is that it has an awesome delay, but seldom do you need all four delay slots going, I typically use one or two of them set to dotted 1/8 and dotted 1/4 values left and right, and the damping control gives you the "shadows" effect as explained here by using a low pass filter instead. It can be a subtle ambience or full on effect.
