Flippant comments aside, I'm entitled to use a competitor's product instead if I don't like how Google is treating me or the changes they are making. This is likely not the goal that Google was seeking to accomplish. I'm sure you understand that Google does derive revenue from visitors, correct?
If they want to A/B test something like that on a signed in, daily visiting member, they should offer a small explanation and an opt in/opt out option.
If people opt in and opt out, then they are testing the interface for people who are willing to opt in or opt out instead of everyone.
Me, I really don't care. Background image? No background image? Who cares. I type something into Google and I get where I want to go. And their other services like Android, Voice, Calendar, and Reader work for me, so I continue to use them. People waste too much time caring about things that don't matter. ("OH NOES, but what if I'm on the moon and really need to Google search! Loading the background would be too slow! You Are Not On The Moon.")
http://www.google.com/corporate/tenthings.html
This background image breaks at least the first 3 of these 10 things.