BlizzCon is the major fan convention for all of Blizzard's games. Past BlizzCons have launched all the WoW expansions, including Cataclysm this last August. BlizzCon 2009 had approximately 20,000 attendees. According to the Convention Center's website, BlizzCon 2010 will be bringing in 30,000 people.
You can place money on the bet that WoW.com will be there covering everything. In fact, we'll meet you at the blackjack tables.
Viva Las Vegas, baby!
Update 4:15 p.m. PST: Blizzard has responded to let us know that they haven't announced any details regarding their next BlizzCon, and that they recommend everyone refrain from making any travel plans at this time. However, the Las Vegas Convention Center has confirmed this booking and continues to list it on their calendar.
Update 10:50 p.m PST: Blizzard has contacted us further and said "As we haven't announced any details about the next BlizzCon, we can say it won't be held in Las Vegas." We're currently in contact with the LVCC and Blizzard, and will hopefully be able to provide more details on exactly what's going on in the future.
Update 9:30 a.m. PST, 11-13-09: The listing from the LVCC has disappeared. However, here's a copy of the page.
Update 12:30 p.m. PST, 11-13-09: The LVCC has retracted their statement. Please see the additional information.