I can't remember ever eating it. I've never ridden a horse either, come to think of it. I'd probably ride or eat one, if it became necessary, although I can't see going out of my way to do either.
In my experience, mammals that are herbivores are usually pretty tasty, but carnivorous mammals are not. It's not that way with fish and reptiles and birds. I'm not sure why. Anyway, horses are vegetarians so I'd expect their flesh to taste, more or less, similar to alpaca, deer, and the like. Texturally it'd be different, but I like jerked meats and I like octopus and conch and even crunchy meats, so the "stringy" or "tough" part doesn't bother me. Neither does flatulence.
What carnivorous mammals have you eaten? Dog?