If you want to open a layered Photoshop file as a flattened image you can save time by going to the Open dialog box in Photoshop and selecting your file. Hold down the Shift and Option keys and hit open. You will be presented with a dialog box asking if you wish to Read the Composite Data Instead. Hit OK and you will have a flattened version of your file opened instead of the layered version. This key-combination works while double clicking a file in the Finder as well.
