Recently, I found that right out of the blue, double clicking a file assigned to open in Photoshop - like .psds, but not limited to those - did indeed open Photoshop, but Photoshop did not, consequently, open the actual file. You could still open files in Photoshop by using its own Open panel, and since the OS X standard Open panel makes it easy to open a file in this way (you can drag and drop a file from the Finder or elsewhere, like proxy icons, into the panel and it’ll open the containing folder and select the file for you), it was still usable, but it was a nuisance.
I tried most things to fix this. I tried Getting Info on a Photoshop file, setting its assigned application to another application and then back to Photoshop, and then clicking Change All, but it didn’t work. I tried temporarily moving away the preference data files so that Photoshop could generate new ones, but that didn’t work either. Black magic was also a no-go.
Finally, I stumbled upon the solution in a desperate fit of “I don’t know why this would work, ever, but LaunchServices is weird like that”. Go to the folder Photoshop itself is kept in, select Photoshop and make an archive (zip file) of it. Rename Photoshop and move it out of the way - like, say, to your Desktop. Unzip the archive you just created. Get Info on a file that opens in Photoshop, and notice that it’s still set to open in the now renamed old copy of Photoshop (because file bindings are persistent and connect to the file’s unique file system ID, and not its path, that’s why). Change the file to open in your fresh new copy of Photoshop instead, and Bob should be your uncle. (Don’t forget to “Change All” after you’ve tried it, so that not just that one file will open in the new Photoshop.)