At the end of "The Northern Air Temple," the fire nation soldiers find the hot air balloon and the general says "this defeat will be the beginning of many victories." Well so far we have failed to see a single victory come to pass for the fire nation from that defeat. Is it being saved for the third season, or has the hot air balloon discovery by the fire nation just been forgotten?
I'm pretty sure that there was at least one other possible major forgotten thing like this that I wanted to bring up here and now I can't think of it...