Nice article by Lukas Mathis on UI elements and amounts of detail required to obtain an optimal design element.

“The history of the visual design of user interfaces can be described as a gradual change towards more realism. As computers have become faster, designers have added increasingly realistic details such as color, 3D effects, shadows, translucency, and even simple physics. Some of these changes have helped usability. Shadows behind windows help us see which window is active. The physicality of the iPhone’s user interface makes the device more natural to use.”

http://ignorethecode.net/blog/2010/01/21/realism_in_ui_design/