Keyboard navigation is too often overlooked in desktop apps. It should be in the very first release. A high percentage of early adopter-types are power users who want that kind of functionality. I can't tell you how many OS X Twitter clients I installed, only to promptly uninstall them (and never try them again) because I couldn't navigate them with the keyboard. The well thought out keyboard navigation was what sold me on Sparrow the moment I installed it.