One thing I think they'd do great is with recurring NPCs- the big bad suffers one of the crits, then next time the party sees him he's got a permanent limp (or shows up as an ally, having been given amnesia from a blow to the head!). Heck, after suffering from some of those criticals, maybe even a lowly orc minion would try to escape, only to turn up at a later time and seek revenge on the guy who carved his initials in his forehead.