The relationship between a document and its owning application is called a preferred application binding. Since the very first day of the very first version of Mac OS X, there has been an uneasy detente between the Unix way of binding documents to applications and the former Mac way, inherited from the early days of the Mac OS. Now, in Snow Leopard, users and developers are complaining that the Unix way is being allowed to run roughshod over the Mac way.
Perhaps the issues we have been seeing relating to Finder's inability (at times) to open files is related to this change (or a bug in it). The article highlighting some of these issues follows:
Some users are experiencing an issue in Finder where files will not open when double-clicked. After upgrading to Snow Leopard these users report that they experience the problem intermittently. Files no longer open in their default application, though using the program's "Open" function works fine.
Apple Support Discussions user "marminio" reports:
Since I upgraded to Snow Leopard, intermittently I have been unable to double click some items to open them in their default programs. I can go into the program and open them via File - Open.Many users report seeing this problem occurring particularly while using Microsoft Word, attempting to open .dmg files or PDF files, and zipped or archived files. ASD forum poster "mattykMPLS" writes:
If I double click an item with it's default program open, nothing happens. If I double click an item and the program is not open, the program bounces in the dock and does not open.
Same for .dmg files. If I download them, I can only open them using Disk Utility.
These problems are not present when I boot up. They only happen at some point later. A restart fixes the problem.
At first I thought it was just attachments in e-mails not opening correctly... Then I discovered that double-clicking, or right (option) clicking and choosing open, or open with, did not do anything. If the default program for that file is open, it will take you to the program but will not open anything. I have found this to be a problem with .pdf, .doc, .docx, .jpg files.Attempted solutions include deleting the com.apple.Finder.plist file, repairing permissions, relaunching Finder, or restarting the computer. While restarting seems to work for most users, it is not a great solution for efficient workflow. One user, however, discovered that the issue may be related to special characters in the file name, blocking Finder from opening the file. User, "msabatino" suggests looking for files with the # symbol or any other special characters and renaming those files.
Another user suggests that a solution may be related to the click speed of the mouse/trackpad button. Changing this option to its slowest setting seems to have fixed the issue for at least one user. To adjust this setting, navigate to System Preferences > Trackpad (or, if you use a mouse, Mouse) and move the "Double-Click Speed slider to the far left (Slow).