Currently by throwing potions of weakness at villagers and then giving them a golden apple, we can change them back, but it takes ages and looks boring. I think it should be changed, and here's how:
For this thread I'll assume that the "curing" works by, once fed a golden apple while weak there is a 1/1000 chance per tick of curing, I don't know if I'm right, but you get the idea.
I suggest that to cure them they go through 4 stages, with a 1/250 chance per tick of advancing to the next stage. Once in the final stage there is a 1/250 chance per tick of becoming a villager again.
The villager emits red potion particles.
The villager's head twitches about once every 3-4 seconds.
The villager's arms shake slightly head twitches are more frequent now, about once every 2-3 seconds.
The entire villager shakes like an enraged enderman, the head twitches every 1-2 seconds.
Finally, in a burst of particles, the zombie infection is cured and the villager returns to normal. All these effects would be purely visual and I think they would make the zombie-villager transformation seem more exciting.
Village Mechanics: A not-so-brief guide - Update for 1.4! Added subsection on iron farming to the iron golems section. Only ten villagers required to spawn golems (down from sixteen)! Put to rest the "facing doors cancel each other" myth!
It takes awhile for them to be cured but I think that's fine. I'm not sure if they'll despawn if you go too far away during this time however, if they can despawn while in the process of being cured then I think that should be removed (as if you cure them you don't neccesarilly want to wait around for it).
As for the way it looks, I don't really care how it looks.