While repeatedly saving a file to overwrite an already existing one, I found a cool little timesaver that's built into OS X's Finder. I'm sure this is old hat for most users out there, but for those like myself that didn't know about it -- it's worth mentioning.
When saving a file, if you'd like to replace an existing file using the same fileneme, just click the file you'd like to replace from the dialog's column view (they will be grayed out) -- and the filename will auto-populate the "Save As:" field. No need to retype the name. It will even append the file extension, based on what file you click.
A small timesaver, but cool nonetheless. And yet another example of the subtle features that Apple builds into the OS. Too subtle though? It sure took me awhile to discover it -- and that was by chance. Then again, I'm not putting much effort into seeking out tips and tricks on a regular basis.