Ever since I upgraded to Mac OS X 10.4 ("Tiger") a couple of months ago, I lost the ability to double-click open Photoshop files in the Finder. I'd double-click on the file, Photoshop would open (or switch to the front) but nothing would happen. I've been living with this bug for several months until I was irritated enough today to find out if it was just me.
As it turns out, it is a known bug and a relatively simple fix if you have your original Photoshop CS disks handy. There are two solutions. One is to reinstall Photoshop CS and the other is to copy a file called "Adobe Unit Types" to your "ScriptingAdditions" folder in your "/Library" folder. More details here in the Adobe Supporrt Knowledgebase:
I wish CS/CS2 would check for the presence of the file at startup and repair themselves (a'la Microsoft). Oh well.