Okay, so everyone knows League of Legends is the most popular game in the world now, right? How that translates into viewership might blow some minds. For the Season 2 World Championship, Riot Games has confirmed that more than 8,282,000 unique viewers tuned in via television and online streams, with almost 2.5 million of that coming from China and Korea. The max concurrency for online streams was over 1,154,000, on top of over 8,000 people in the live audience at the Galen Center. All glory to the future of eSports.
To be fair, I should note that capacity for the Galen Center was said to be 10,000 people, so the live audience fell short of selling out. [Edit: Riot has updated me that the World Championships did in fact sell out of tickets -- less than four days after going on sale, no less. The 10,000 number doesn't consider the statium arrangement that Riot had set up in Galen.] Still, considering eSports hasn't particularly evolved as a live event, 8,000 people is still quite many. A further base of comparison is Dota 2's The International 2 event, which had a confirmed 567,000 viewer count. League of Legends and Dota 2's prize pools were $2,000,000 and $1,600,000 respectively; it's safe to say the MOBA business is good right now.
It's a good time to be an eSports spectator right now. Dota 2's SLTV Starseries tournament just wrapped up, and was definitely one of the best tournaments yet for the game, and League of Legends' IPL 5 tournament begins at the end of November. There's literally more and more to be seen of these games every month. My bet is that it's only going to get bigger.