For starters, the default background image is scaled according to the content mode (if there is no default image). There are 4 states in which you can set the background image for "Default, Highlighted, Selected, Disabled."
You can set a specific action for any of the touch events listed on the 6th tab under the inspector (on the right side of my Xcode 4 setup). To do this, simply click and drag to the intended receiver. You do not need to click or right-click (this will not work from the inspector)
When you press Ctrl or right-click and drag the actual button in a hierarchical or layout view, by default it sets the purpose and action for Touch Up Inside
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