The Google UK logo today is a mass of bouncing colourful balls that flee the mouse (screencast):
If you reverse engineer the code you will find that the bubbles are actually DIV elements that have a huge border radius. You can find the whole code of the effect in the source code when you look for google.doodle() or in this gist (beautified):
As you can see there is not much magic to it. The CSS is even easier:
Yes, all of this is pointless bells and whistles, but I have to say I like it that a company puts technology and showing it off just for a day on their agenda.