Blizzcon 2011 opening ceremony rolled out with minor bits about Diablo 3 (box art, collector's edition contents), but the most interesting news is that Blizzard clearly recognizes that with the launch of Diablo 3 and the inevitable six-to-nine month time without updates to World of Warcraft before the next expansion, people would probably unsubscribe to World of Warcraft for a good while.

So they are offering a deal - World of Warcraft Annual Pass

Subscribe for 12 months and receive free Diablo 3 digital download (when released), a guaranteed spot in the beta of the upcoming World of Warcraft expansion and a special in-game mount. The offer is available immediately.

That should definitely help Blizzard fight the inevitable loss of subscribers that usually happens during the final months before a new expansion. In fact, this may turn out to be so popular that they may have to set up additional servers for the beta of the upcoming expansion.