I have food poisoning from one I just went to. Thank goodness the simultaneous vomiting and diarrhea held off until I got home. I was a bridesmaid and I don't think my dress would have enjoyed that very much. It was a breakfast potluck the day of because it was a DW in the middle of nowhere.
I hate potlucks so much.
EDIT: I posted this from the toilet.
SECOND EDIT: The number 2 reason not to have a potluck at your wedding, it's rude as hell.