Membranophonist’s Ramblings

See, you got four extremities, you got left hand, right hand, left foot, right foot. You ain’t supposed to let your right hand know what your left hand is doing, your left foot know what your right foot is doing.

Art Blakey in an interview with Ben Sidran

Match a graphic element with a user’s likely expectations of its behavior. Don’t change the meaning or behavior of standard items. For example:

• Always use checkboxes for multiple choices, not for mutually exclusive choices
• Use push buttons for immediate commands such as ‘Open’
• Avoid using push buttons to display pop-up menus or serve as tabs
• Avoid using bevel buttons as tabs

Emphasis mine

Apple HIG: Human Interface Design Principles

From the 10.4 Print dialog:

From Mail 2.0: