Google’s Personalised home page now comes with themes so you can basically change the banner of your home page. There are a couple options to choose from at the moment and what I like about them (certainly the beach one) is that the themes can be tied into your local time and will apparently change depending on the time of day.
Steve Rubel made a good point that these changes, while pretty, may also open the door for sponsored layouts. Marketers could be sold space to create branded themes on the site. Now that is a captive audience. Every morning a group of people start their web browser and see your branded theme on their desktop. You could take it a step further and start adding advertising based on theme choices. A person who picks, say, a Nike theme may be presented with sports advertising based on their preference for a sports theme. Now there are no ads on the personalised home pages but this could change. An alternative could be to track who selected which theme and customise advertising on subsequent pages? Am I reaching?