Previewing files and pictures on Leopard

If you do not have Leopard or Snow Leopard then this will not be any use to you, sadly.  To preview a pages document, a keynote, a picture (and many more things) just hit the space bar while the file/picture is selected.  This is very handy if your checking what files/pictures are but can't see what the thumbnail is.  Another cool feature of this is when your previewing a image/file below the preview there's a fullscreen button, click it and the preview will go fullscreen.  Yet another feature of this is if you have say a folder of twenty photos and you want to quickly see each one to find the one your looking for you just click on the top one and hit space.  Once the preview is up you can use the arrow keys while in preview to flick through the pictures!  (This will not work in fullscreen mode)

So, you may ask, why can't I just do everything in preview and never open something again?  Well, for a start with documents and pictures you can't edit in previews only view.  And secondly the quality isn't as good and in things like keynotes you can't view it properly, no effects or anything, you just view it like a pages document.