I've been using Generals exclusively as Warlords for the upgrading ability and the 20XP. But.... I didn't realize that the instructor feature of +2XP was Cumulative!
Which pretty much breaks the game. Thats why I never use that. I prefer Warlords since I enjoy having specialized, uber unit leading my war efforts.
Also, why doesn't America get any strong unique plane units? If any Civ should have an advantage in the air late game, it should be America. Their UU are quite lacking.