I'm really liking the UI/UX concept behind the new Sparrow mail application. It's a clean, minimal setup that reminds me of Tweetie in more ways than one. And that's not a bad thing, as I think Tweetie is hands-down the best solution for the Twitter content it provides. Could Sparrow be an effective new way of thinking and handling mail? Quite possibly so. The few downsides I see are the lack of filing mail into archived categories or finding mail that has been archived somewhere. It seems to work well for an Inbox / Outbox style of thinking but not so much for a Filing Cabinet style history. However, that may change and the clean look is appealing enough to keep an eye on it to see how they grow and improve.