I don't normally play two FF's all the way through from start to finish at the same time. If I am still attempting 100% completion for one FF then I may play it from time to time while in the middle of another FF story.

I also tend to play a fighting game or other uninvolved genre's while playing a main game(usually a RPG). I am also a consistent Gears of War 2 online player. So, I do try to stay interested in my gaming side by holding interest in several titles at a time.