The UI language features a great deal more separation of code and design than the arc web framework. I know libraries aren't a high priority at the moment, but this guys UI is pretty expressive. To be honest, I wasn't expecting much from the demo app, but it had a very rich presentation layer, and his actual code was very simple.
I'm definitely the wrong man for the job (inexperience) but I imagine that something like this, written in Arc, would be the perfect showcase for Arc's succinctness/power.