See my update below, Google basically pulled the background images.
At midnight of June 10th, Google flipped the home page of Google.com to automatically show a background image. They announced that this will only be automatic for June 10th, a 24 hour period.
Lots of people are calling it a Bing impersonation, which I assume Google knew and decided they didn't care about.
But at the same time, although I personally like Google really pushing people into the customized home page - I think they should have given an opt out. I think most people had no clue that this was an option until Google went this drastic route, but give them a way to opt out.
I was browsing the Google Web Search Help forums and the first 6 pages of threads in that forum, as of 8am (EST) are all complaints. Here are the first 3 pages, I ran out of room...
Google, when doing something this drastic, next time, just put an option to go back.
Forum discussion at WebmasterWorld, DigitalPoint Forums, Google Webmaster Help and i'll just link to one Google Web Search Help thread.
Update: Google removes background images early and adds a link explaining things. Google's Marissa Mayer tweeted they just removed it. But she did not explain why. I assume it has to do with the complaints.
Actually as of now :) @Jon_E Google search background back to normal tomorrow, says @marissamayer.
Google updated their blog post saying:
Update June 10, 11:31AM: Last week, we launched the ability to set an image of users' choosing as the background for the Google homepage. Today, we ran a special "doodle" that showcased this functionality by featuring a series of images as the background for our homepage. We had planned to run an explanation of the showcase alongside it-in the form of a link on our homepage. Due to a bug, the explanatory link did not appear for most users. As a result, many people thought we had permanently changed our homepage, so we decided to stop today's series early. We appreciate your feedback and patience as we experiment and iterate.