Go to your Google Search App on your smartphone and Google the words, [Up, Up, Down, Down, Left, Right, Left, Right].
Google will respond in voice saying, "Cheat Mode Unlocked Unlimited Free Google Searches."
This only works when you speak your query either from the Google Search App or Google Search page from your smart phone, or via a Chrome browser that has voice search enabled.
Here are videos of it in action on both an iPad using the Google Search App and Chrome on a Mac from the Google home page:
I spotted this via Pierre Far, who works at Google but seems to have stumbled upon it randomly. He posted this on Google+.
Forum discussion at Google+.