How many GMs allow these? how do you handle them?
It really depends on the game really.
If it is just a quickie 1 shot, then I may not allow them since they are milked easily and serve on real purpose. For a long term game, I'll allow them, but make sure that they make sense. And if they do choose NQs, then I will ensure that those NQs (and the PQs as well) actually are involved in the gameplay, this is especially true for the ones that are huge NQs. AI in house, I'd have them being really annoying but it wouldn't really play a huge factor most of the time (although occasionally I may have the AI keep them awake all night to either force them to run their character tired, or find somewhere else to sleep.