Android

I've found the look of the UI to be an acquired taste, and maybe easier to swallow if you're used to using open source stuff. But I'd agree that the way it works is, in places, almost unforgivably unfriendly.

But it's the "almost" that keeps me using it, because there's nothing else that works across the platforms I care about, even if the application is so, so difficult to recommend or "deploy" to users.