Generally, when you open a file, the default program for reading that file will launch and load the file; however, opening a file either in the Finder or in the Dock in Snow Leopard may not open the default application. The application may launch and then become unresponsive without loading the application.
Apple discussion poster "Julian." writes:
"After a while of operating, if an application isn't launched and i open a file of that app from the Finder or the Dock, the app's blue indicator blinks for a very long time and when it's finally open the app freezes. only option is to force quit the app. But i can in fact open the file, if i open the app first and then select the file with the open dialog. This happens with every application: Archive Utility.app, TextEdit.app, Preview.app and non-Apple apps."
Despite these freezes, if you open the applications yourself, they launch just fine and can then be used to open files from within each using the File Menu → Open option. It is just when files are loaded from the Dock or Finder that the freezes occur and the files cannot be loaded.
While this is not a widespread problem, affected people have found that this occurs after launching the QuickTime X Player. When this happens, it seems to freeze the core service that is used for displaying alerts and other system windows.
To clear this problem if it happens, run the Activity Monitor and quit the "CoreServicesUIAgent" process if it is running. This should return Mac OS X's document handling functionality to various programs, at least until the process hangs again.
Some people have reported success correcting the issue by running OnyX or other system cleaning programs to remove all temporary cache files as well as rebuild services such as the launch services. Basically, running all available maintenance routines seems to help, though specifically rebuilding the launch services, clearing the dyld shared cache, and running all system and user "cleaning" routines should be done.
Unfortunately, there's not much more information available about this problem, so it is hard to troubleshoot; however, since it seems to be spurred by QuickTime X, you might look at third-party add-ons for QuickTime that you may have installed, such as Perian or Flip4Mac. Try removing these from your system and restarting the computer into Safe mode to see if the problem persists when QuickTime Player is launched. Then try booting normally to test the system set-up.