From the NCAA 2006-08 Men & Women's Ice Hockey Rules and Interpretations, Rule 6 Section 18:

"A goal shall be allowed if the puck has been directed into the goal by an attacking player with the skate, unless a distinct kicking motion is used."

Sadly, there's no further clarification on what makes a distinct kicking motion, though based on tonight's game it seems to include a puck hitting a foot that isn't moving towards the goal. Dammit.