Zen is actually solid these days. being a Firefox-based browser, it has its quirks, (i.e. Theo complained about gradient rendering or whatever, but who cares?) but it's still the best Arc-like we currently have.

plus, you get synchronization across desktop (Zen) and mobile (Firefox for iPhone/Android). since Google limited theirs only to official Chrome, this feature is basically exclusive to Firefox and forks, Arc <-> Arc Search, and Chrome for desktop <-> Chrome for mobile.