I won't not patronize a restaurant that doesn't take AMEX, but I won't become a regular at that restaurant because of it.
I eat out almost every night. AMEX is the first card out of my wallet. I am real whore when it comes to points. I am also obsessed with iDINE. Between both I have earned many, many, many points/miles. Enough to fly quite a few people to my wedding (first class) in a couple of months. In South America. Those points add up.
I ate last week at a restaurant called Les Enfants Terrible on Canal Street in NYC. Good French/African food.
ANd how did I pay? AMEX. Why? That's the ONLY card they take.