There are two kinds of cripple, in my opinion. The first is temporary, such as from a broken leg or the like; the second is permanent, such as when you're hamstrung.
This leads me to laugh every time someone gets hit with 'hamstring' or 'crippling shot' and is immediately walking again a few seconds later.
I want to suggest that the mechanics of it be re-worked so that you have to heal yourself (EVERY class has a self-heal) or be healed for the condition to go away.
Naturally, a few skills might need to be adapted... but this way the condition would actually make sense >_>
P.S. This would also punish those stupid enough not to bring a self-heal, which is a good lesson for everyone.

<EDIT>: Such spells as Ethereal Burden and the like can logically keep their duration-cripple.