Go to your iPhone or iPod Touch, open up mobile Safari and search for [tilt]. Look at the results. Do they look like they are tilted a bit to the right? They sure do to me and everyone else searching for tilt on mobile Safari on the iPhone.
Here is a picture:
I am not sure if this is a Google prank that went unnoticed over April Fools Day or if it was an Apple prank. I tested this on Android phones and it does not have the same effect.
Personally, I find this to be very funny.
Forum discussion at Google Web Search Help
Update: This should work on Android devices as well and this was an April Fools easter egg that was designed by Google and is still available for users to play with.
I believe the first to spot this was @iPhoneTwitter. Very nice find!