Here are some screenshots of my computer running Beryl.
The customary Cube:
Windows can be made to look like a negative(Konqueror here) and so can the complete desktopHave too many windows and don't want to Alt+Tab, get a view of all the windows on all desktops or on current desktop depending on which screen edge you take the mouse too(configurable)
Transparency. The Konqueror window on top is partially transparent(Alt + mouse scroll) and shows the blogger window beneath