TweetBot is sexy, no one can deny it. One of the coolest aspect of TweetBot is the unobtrusive panels that show what is happening on the app. Some apps like Reeder have resorted to HUDs. The problem with HUDs are that, they are shown on a different "z-index" and human eye has to shift the focus to read what's on it. For the same reason, HUDs feel a bit disconnected from the UI which could be why on both iOS and Mac, Apple uses HUDs to show global system level notifications.