I used the following script to symbolize the crash report I got from the user:
/Developer/Platforms/iPhoneOS.platform/Developer/Library/Xcode/Plug-ins
(Xcode 4.2) symbolicatecrash is a perl script that uses spotlight to locate the dSYM files that belong to the app that crashed. If you run symbolicatecrash with the -v (verbose) option you'll see something like: Searching in Spotlight for dsym with UUID of ... Running mdfind "com_apple_... == ..."
So, be sure that spotlight works, and the indexing for spotlight is active for the volume where your stuff is located, with the mdutil command: mdutil -s -a If the volume your archived Apps are on is not indexed be sure to switch indexing on. (As root/sudo: mdutil -i on /Volumes/...)