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!

Comments:
Sarah Van der Veken
04/06/2011 01:41 pm
It works on my Android 2.2.1 HTC Desire HD with the standard WebKit-based browser.
Jody Cake
04/06/2011 02:23 pm
it looks like it is a April fool's that Google did for their Mobile version that people overlooked or missed..works on android and also works on my PC by using the google mobile site and searching for tilt... http://www.google.com/m or http://www.google.com/m/search?&q=tilt for the direct link to the Tilt search results
online coupons
04/06/2011 02:33 pm
Is it just for the sake of fun? or perhaps there might be some problem. 1st April gone, now this should not be happen again.
Barry Schwartz
04/06/2011 02:34 pm
I doubt it is a bug. :)
Barry Schwartz
04/06/2011 02:34 pm
Nice find on the URL.
Mordy Gilden
04/06/2011 03:27 pm
http://www.youtube.com/watch?v=nxAljETtjzw Just tried it on my Froyo device and quickly videoed it. Its clearly an Easter Egg, and I think will come up on most mobile browsers (will check standard feature phone browser later today). Nice find! Annoying bit? Scroll to the bottom, you actually can't see the left side at all anymore! Good one!
IPhoneTeam Twitter
04/06/2011 04:42 pm
I think I should be properly credited for this, I couldn't find it anywhere else on the web and you didn't state any sources: How about this one: http://twitter.com/iPhoneTeam/status/55509481005662208
Barry Schwartz
04/06/2011 04:44 pm
Updated my post… Hard to figure out who spotted this first. But you seem to have tweeted it before anyone else. Very very nice find!
OnlineJoe
04/06/2011 08:05 pm
Hay Guys Try the same on " Crooked" ! Nice catch!
IceBeam
04/07/2011 04:13 am
But why not on normal Android! Where do I register a complaint?
Rajsingh2505
04/08/2011 03:20 am
It does do the same thing on my Galaxy S (Android)
AndroidUser
04/19/2011 04:58 pm
It works on Android. At least on mine.