If you use the menu bar's Airport icon primarily to turn Airport on and off, you can save some space by getting rid of the icon and toggling Airport power with the keyboard or mouse instead.
Sometimes it'd be handy to view a single PDF file in two windows. But generally speaking you can't open the same document twice in a single app. Here's a way around that restriction.
Have a link to a downloadable file, but don't want to open your browser to fetch it? Here's a service that'll do it for you in a snap.