OS X Productivity Tip : Keyboard Shortcut for Zoom
Quick and easy tip: I find myself using Preview.app quite a bit to read documentation (in addition to normal development tools), and usually zoom the currently active window to fill up the screen. Using the mouse in this case gets fairly tedious, so I took to mapping this command to a keyboard shortcut. While the mechanism for doing this is nothing new on OS X (it's been around forever), few people seem to take advantage of it.
Mapping a keyboard shortcut to the Window->Zoom command (in Windows, this is uniformly accomplished via "Alt-Space + X") helps a lot to quickly zoom in/out of whatever it is I am doing, but many OS X applications do not map this command by default. Enter the Keyboard & Mouse preference pane. This single change happens to work with many applications (Mail, iCal, Safari, XCode, etc). I find "CMD-/" to be a fairly reliable and easy to remember mapping.
This is a screenshot of a section in the "SystemPreferences->Keyboard&Mouse->KeyboardShortcuts" preference pane. As you can tell, I generally don't customize my system that much, but this one is a no-brainer. Give it a spin and see how you like it.