Text (AR+errata): At the beginning of each opponent's end step, if that player didn't cast a creature spell this turn, put a 2/2 green Lizard creature token onto the battlefield. [Oracle 2009/07/08]
Due to the intervening "if" clause, it does not trigger if the player played a creature spell this turn, and it will be countered on resolution if the player somehow plays a creature spell prior to resolution starting. [Alara Reborn FAQ 2009/04/30]
If a creature spell was played and then countered before it resolved, then a creature spell was still played. [Alara Reborn FAQ 2009/04/30]
