If you thought Brawl online modes were pretty neat, you havent yet played Mario Kart Wii. As well being able to play with more than one player online at a time, Mario Kart Wii fixes two of Nintendo fans complaints about Wi-Fi Connection. You can now fill your friends list to 40 in two exciting ways. First off, you can send an invite via the Mario Kart Wii channel to invite friends on your consoles Friend Code to your Mario Kart Wii list. The other method is simply adding a friend post-race with anyone. No trading codes, just a simple addition to your list.
Source: Nintendo Europe