The new Spectator mode lets you watch and bet on other people's online matches. Yeah, on the Wii.
Super Smash Bros. Brawl continues to establish itself as an online experience with features you'd expect in a PC or Xbox 360 game, certainly far beyond anything yet seen on Wii. The newest announcement is Spectator mode, in which you can watch Wi-Fi matches of anonymous players from around the world. As you play your own online matches, you have the option of allowing spectators, which means that data from your battle will occasionally be recorded by Nintendo's servers. Spectator mode will continuously play back matches collected from players in this way. The feature acts like a global sports channel, as everyone in Spectator mode will see the same match being played at any given time.
You aren't just limited to watching, though. Prior to each match, you'll have the opportunity to bet coins on which player you think will be the winner. Naturally, a correct guess will be rewarded with some multiple of the coins that were bet. As of this writing, the purpose of gold coins has yet to be announced.