Welcome to the pr0n index!
This is a very silly web application that tells you what percentage of the internet for some given search phrase appears to be about porn. Hours of amusement can be found in searching for names of your friends, their mothers, pets, etc.
It works by searching Google Images both with SafeSearch On and Off. It'll take a difference in the estimated result count and return the percentage that only appeared with it turned off. It's dead simple, and hugely flawed, of course, but none of this detracts from the hilarity.
So click "Back" and give it a try, then tweet to all your friends the interesting pr0n indices you've found!