Phelpster at The Manchester Morgue posted about this the other day, so I thought I'd give it a try.
Here's the link to get Simpsonized. It seems to be a very busy site. If the server is busy, you'll have to try again later. If you manage to get on you'll have to upload a picture of yourself and then tweek it to get turned into a Simpsons character.
The accompaning pictures are me, my wife, my son and my nephew. My son's picture looks the most like him and my wife's the least.