Open Transport vs. QuarkXPress -- I've heard reports of two conflicts between Open Transport 1.0 (shipped only on the Power Mac 9500s) and QuarkXPress. If you have an XTension installed that receives the XT_NETRECEIVE opcode, QuarkXPress will hang on launch. I doubt there's any easy way to determine if you have such an XTension loaded other than by empirical testing. Apparently, Open Transport 1.0.1 fixes the problem. Even with Open Transport 1.0.1, if you have either the printer port or the modem port chosen as your network connection in the AppleTalk control panel, QuarkXPress will hang on launch if any XTensions that use network serial copy protection are installed. [ACE]
Option-click to Hide Apps Quickly
This trick has been available in the Mac OS for years, but many people still don't know it. If you have too many windows cluttering up your screen, you can hide specific ones easily as you work. When you're in any application, hold down the Option key and click on another app's window, on the Dock, or in the Finder to switch to that other app and simultaneously hide all the windows in the previously current app.