LittleBigPlanet. He demonstrated how easy it is to make your own levels, customize in-game and user created levels, create your unique sock puppet character, win game elemets, and have your personal world ranking on the PlayStation Network.
Alex showed PlayStation Eye integration, which will most likely include YouTube upload integration. He briefly mentioned the Trophy System also.
It looks like it will be an easy task for anyone to re-create Super Marion Brothers with LittleBigPlanet, the question is who will be first to do it in the fall.
Trophy System mentioned
SMB Level Reference
[Source: Sony PS3 Modding - Homebrew, Upgrades, Mods, and Hacks]