I heard it was like 1/16 or something. Meh.
I've only gotten Celes' Desperation Move before, it was kinda cool. (I was fighting Kefka for fun, and then I just made Celes attack because I knew he was almost dead and she just sliced him for 9999 damage. xD)
Here's all the characters and their Desperation Attacks, if you wanted to know.