I strongly feel that true utilitarianism is a decoherent idea (it doesn't really work mathematically, if anyone wants me to explain further, I'll write a post on it.)
Because of interpersonal utility comparisons, or what? That might affect some forms of preference utilitarianism. Hedonistic and "objective welfare" varieties of utilitarianism seem like coherent views to me.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.