Ted Landau wrote a pretty cool Geek Factor article for the July 2004 Macworld. In it, he explained how to change the standard "unexpectedly quit" dialog box, as you can see at the right. Caution: This hint involves modifying a system file. It shouldn't cause any problems, given that it's a text file only, but still, proceed at your own risk (and you do have a backup, right?).
Creating these customized messages is quite easy, as Ted explained in the article. The messages are stored in a file called crashdump.strings, located in this directory: /System -> Library -> CoreServices -> CrashSubmitter -> (Control click and select Show Package Contents) -> Contents -> Resources -> English.lproj. However, these are system-owned folders, so you'll need to do a bit of permissions work to modify crashdump.strings.
Start by navigating to and selecting the English.lproj folder that holds the crashdump.strings file, and then do File -> Get Info (Command-I). In the Ownership & Permissions section of the Get Info box, click the triangle next to Details, and then change the Owner pop-up from System to your (admin) user. Enter your password when prompted. Leave the Get Info window open.
You can now modify the contents of the English.lproj folder, so start by making a duplicate of the crashdump.strings file (select it and hit Command-D), just in case you want the original back at some point. Now drag and drop the original file onto TextEdit (or double-click it if you have the Developer Tools installed, and it will open in XCode). Change the messages that you see as you wish -- leave the %@ bit alone, as that represents the program's name. Also note that you can force line breaks with a \n entry. Once you're done editing, save and close the file.
Return to the Get Info window you left open, and change the ownership of the folder back to System. Now all you need is a program to unexpectedly quit, and you'll see your new messaging. If you kept an older copy of the Developer Tools, you can find a program called Bomb.app, which does nothing but unexpectedly quit (it's what I used for the above screenshot).

