We've been using the Warner Marine Ultimate Snow since it was released, and its amazing how clear it can make your water. We use it alone, not "loaded" as they also recommend, to carry off excess nutrients to the skimmer, and it works awesome. There is a point of over-dosage though... It seems that this has the ability to actually strip the water of too many nutrients, which can potentially bring on cyanobacteria. Use it, but use it sparingly...
I know other people are "loading" it with Aminos/etc, but we've haven't toyed with that area much... Maybe they can also chime in. Or perhaps Jon might have something to add?