Yesterday saw the biggest change to the Google homepage since 1998. They replaced the minimal, functional and revolutionary design of the original - which has remained largely unchanged for 12 years - by adding a Bing-like background image that you could change, but not remove.
Now, a few hours later, Google normality is restored; the ‘Change background image’ link is there, but it's something you opt into rather than not being able opt out of.
So it turns out this was a ‘24 hour experiment’ to publicise the feature which, when you think about it, had to be the case otherwise Google's famous themed logos would have become redundant, and that would seem very odd given their popularity.
Still, it's surprising that Google appears to be so afraid of the growth of Microsoft's search engine that they decided to do this.