Twitch is a live video streaming website, it is mostly used by gamers to stream their game plays...
More than 55 million visitor/month. It's like the Youtube for Gamers, because they can stream their gameplays, too.
> Twitch is the world's leading video platform and community for gamers. We want to connect gamers around the world by allowing them to broadcast, watch, and chat from everywhere they play. <
http://www.twitch.tv/p/about
I think that they're really important and you can find some stats there --> http://stats.twitchapps.com