Send your Sims over to your friends for new adventures!
I spied an official Sims 3 Showtime preview of how the Simport feature will work. In this four minute video, two Sims 3 producers walk you through the process of using Simport, and explaining how it's going to work.
Simport is the big breakthrough that the Showtime expansion pack has been teasing about for ages. As I suspected, you will not be able to personally go over to your friends' Sims' houses and play with their stuff (the way that you can with The Sims Social game on Facebook). Instead, you will be shipping your Sim off to your friends, who will have your Sim show up in their game.