Since yesterdays shortcut had to do with the Eyedropper, it makes sense to me to follow with shortcuts for the Color Sampler tool. With the Eyedropper tool selected, Shift-click in the image area to set a Color Sampler. With the Eyedropper tool or the Color Sampler tool selected, Option (Mac) / Alt (Win) Shift-click on the Color Sampler (the icon will change to a pair of scissors) to delete.
The Eyedropper has been relocated to the first grouping of tools in the tool box. In addition, it has been refined n Photoshop CS4, allowing you to choose to sample the Current Layers or All Layers (in the Options bar). The eyedropper’s “Sample Size”, set in the options bar, affects the Magic Wand, Magic Eraser and the Background Eraser. Option (Mac) / Alt (Win) click the Eyedropper to select the background color swatch (instead of the foreground) in the Tool panel. In addition, in Photoshop CS4, the Eyedropper can sample a value of a color within a Smart Object. The eyedropper can now sample colors from outside of Photoshop. Make the color visible (on the desktop, in another application etc.). Then click with the eyedropper on the image and then drag to sample the desired color.