The new Adjustments panel in Photoshop CS4 (Window > Adjustments) contains seven categories of adjustment presets. These adjustment presets can help you learn you to use the various adjustment options, or to quickly achieve a particular effect with a single click.
To use an adjustment preset, just click on one of the right-pointing "flippy triangles" next to one of the categories, then click on a preset.
Here's a handy shortcut, that lets you quickly browse through all the categories at once: option-click (Mac) or alt-click (Windows) on a flippy triangle, and all the categories will flip open at once.
This definitely falls into the "now how was I supposed to know that" category, but is a useful shortcut!