Sparrow has a clean interface, but very poor functionality. There is no support for Exchange, no calendar support, cannot use contacts, either locally or from the server. Its just bare bones stuff. Unless someone fancies a Twitter look, and willing to let go that one cannot configure this mail client with any settings, and still wants to have it because it looks like Twitter, it might just work for them, or else, there is nothing else going for Sparrow. This is a case where looks score more than substance. Completely misguided approach to design.