Are simple tasks taking longer in CS5 than CS4? Check out this tip fromMac Performance Guide: Edit your Preferences and adjust your Cache Tile Size to optimize your setup for the kinds of images you work on. MPG suggests just cranking it to 1024 and forgetting it. What works for you?
Have you explored the blend modes available in Photoshop? If so, you can get to most of your favorites by using a shortcut: Shift + Option/Alt + (first letter of blend mode). For example, Shift+opt/Alt+M changes the current mode to Multiply. The shortcut list isn’t complete, but you can round out and update the shortcuts by changing them in Photoshop’s preferences dialog.

Got phone wires in the way of a beautiful sunset? Use the Pen Tool to create a path along the wire, then stroke the path with the Spot Healing brush. Just make sure to set the size of the brush and the Content Aware option before applying the stroke. Make it faster by recording an action to set the size, options and stroke, then assign that to a hot key!