When Google Moon was originally created, it was tied to an April Fool's Day joke. Zooming to the maximum magnification on the moon's surface revealed a picture of cheese.
Since then, Google became the sponsor of the Google Lunar X Prize for landing a privately-funded vehicle on the moon. They've upgraded the interface for Google Moon and replaced the original low-quality images as better photos became available.
Google Moon is available on the Web at moon.google.com