Well, I have had one-night stands with some of my friends, but I don't think that counts. There was never any conversation where the "let's have sex with each-other but never get romantic feelings" agreement was reached. It just sort of happened, and then it either changed the dynamic of our relationship, or it didn't, in which case we just left it at the one time.
I mean, if people want to try it it's no skin off my nose, but I really don't see it working for the vast majority of people. For one thing, having that sort of strict arrangement between two people has always struck me as an ironically un-casual way to approach the concept of casual sex.