Taking Screenshots

I have taken a few screenshots before on Mac OS X, however I can never remember the short-cut key. Everytimes I just have to look up on Google to find out exactly which key I should type. Therefore I think it will be a good idea to actually write it down somewhere so I won't forget...

Apple + Shift + 3Takes whole screen.
Apple + Shift + 4Takes what you drag and select.
Apple + Shift + 4 + SpaceTakes window.

The above methods will save the content into a PDF file on the desktop. Alternatively, holding Ctrl + above combinations will save the content into pasteboard, and then you can use Preview to export the pasteboard into various graphics format.

Why does Mac have so many keyboard short cuts!