Here’s a short, but insightful article from Minimali.st about making your application’s user interface invisible, which is a goal for interface design on the iPad. The gist of it is that users want to focus on content, not the interface, so make interface controls as invisible as possible while emphasizing the actions those controls perform. One way to de-emphasize buttons is to remove the stylistic touches (color, gradient, shadow, etc.) from less important ones and only stylize the buttons with the most important actions to draw attention to that action. Read the full article here: De-emphasize User Interface Controls.