My life saving shortcut is the ability to undue my obvious mistakes!
Command “Z” on Mac and Control “Z” on Windows. I am working on a Mac using Photoshop CS5 which allows one step undue using Command “Z”. If you hit it twice, it reverts back to your last step – so it can give you and last step – previous step – last step opportunity to check out what you did. If you need to go back more than one step, you will have to click on “History” from you “Windows” pull down file in the main menu and then choose which steps you wish to revert to.