how long can you marinate shrimp for?

Most shrimp marinades I have come across require no more than 15 minutes tops - this is particularly true for Asian dishes.

I wouldn't chance more than an hour, and in this case, I think less is better.

I've marinated shrimp (large ones) for an 1 hour, without the acid "cooking" the shrimp or the texture going weird.

I don't think you want to marinate them for more than 30 minutes - especially if the marinade is high in acid.