Put this in the location bar of your web browser :
javaFOOscript:document.body.contentEditable='true'; document.designMode='on'; void 0
(due to security on my blog, please remove the FOO string)
Now you can tweak and test your design, change text, resize pictures, resize tables, ... so it's easy to review your layout live with your customer during a meeting, deface a website you hate or... just having fun!
Go ahead, test this and play with my blog!