Unlike the Windows system tray, the Mac menu bar provides few options for customizing it to your liking. Here's how to hide your menu bar to free up an extra 20 pixels of precious space and create a cleaner desktop.
After reading our feature-by-feature comparison of Windows 7 and OS X, in which we noted that the Mac menu bar is "fixed to the top of your Mac's screen with no easy way to hide it," reader J writes in to point us toward an old Macworld step-by-step guide for doing just that—though, like we mentioned, it's not as simple as doing so with the Windows system tray. Using this method, you can set your menu bar and Dock to automatically hide on an application-by-application basis. For example, if you edit your TextEdit PLIST file using this method (which I did to test this), your menu bar and Dock will automatically hide when TextEdit is the active application. To see either, just hover your mouse to the respective edge of your monitor. For other apps, your default behavior will remain.
The tutorial requires you to edit a Property List (or PLIST) file, which is serious business, so backing up your original PLIST file is probably a good idea. Since MacWorld's instructions are a little out of date, here's how it works in Leopard:
Find the application you want to turn on Dock hiding for, then right-click or Ctrl-click the application and choose Show Package Contents.
Once inside, double-click the Contents folder, find the file named Info.plist, and double-click that to open it with the Property List Editor.
Now select the Information Property List entry and click the Add Item button.
Enter Application UI Presentation Mode as your new Key, then tab to the Value, enter the number 4, and then hit Enter. The value will change to "All Suppressed."
Save the PLIST (Cmd-S) and launch (or re-launch) the app whose PLIST you were editing. Your Dock and menu bar should automatically hide. How clean!
It's a bit convoluted for simply hiding your menu bar, but it's a handy tip, especially if you have an application that you always use for presentation purposes or you just want a totally clean desktop. As for the Dock, you can easily set your it to always hide by right-clicking the Dock and toggling the Hide option. Previously mentioned MenuShade achieves a similar menu bar hiding effect across your system if you'd like an easier (but slightly less effective) solution, or if you've got your own, better method, let's hear it in the comments.
How to hide the menu bar and Dock [Mac OS X Hints]