Re: would you marry a “mentally challenged [retarded]” person knowingly?
Okay maybe we should just call them ‘special’ 
On the original topic, I have never once seen a real life example. I have however seen a case where the person got duped into marrying someone who I wouldn’t say is mentally challenged (because she can be fine when she wants to be) but she’s just plain old crazy.
Marriages like these only happen in Bollywood, where the ugly retarded Hrithik gets with Preity Zinta.