And here goes the confusion. Angie says, "Upcut pulls the chips towards the router so use if it's a blind hole/slot". The PDF that Stick posted says, "DOWNCUT Bits (naturally) cut downward (away from the router base). This motion gives grooves, dadoes, rabbets, shallow mortises and plunge cuts a smooth clean edge. REMEMBER: Downcut bits push sawdust into the cut. Making multiple passes reduces the buildup of sawdust in the groove."
Wouldn't a dado be a slot? It seems that these two recommendations are at odds with each other, and Angie's recommendation makes more sense to me.
Scotty: I can't change the law of physics! I've got to have 30 minutes!