From the Google Blog:
Today we're releasing six themes for the personalized homepage that try to solve these challenges: a city, a teahouse (super cute -- this one is my favorite), a winter scene, a sky, a beach and a bus stop. All of our themes are dynamic: they change with your own local time of day, current weather conditions or season. If you add the beach theme, for example (changes with time of day), it will ask you for your Zip code and adjust itself to match your local sunrise and sunset times. So if you happen to be stuck in a windowless office, you can at least crack open a cold one and watch the sun set over your desktop.