I usually leave my laptop switched on when I'm not using it, as I'm sure many others do too. A default sony greenish/blueish/redish screensaver popped on after a few minutes...as it has since I bought this machine Time for a change, I thought...into the 3D realm!
Remember that most of these are only demos. The full featured version of them is available at small fee. For those who have a passion for 3D and want to bring their idle desktops to life, these screensavers are well worth it.