According to a news at Gamesindustry.biz, Rop Pardo, Executive Vice President of Game Design at Blizzard Entertainment, confirmed in a question and answer session at the Games Developer Conference this week that Blizzard is going to announce a new game at the WWI this year. He said:

“So you want me to announce the game before [...]

As promised we will be live at the WWI 08 in Paris to inform you about the latest news and rumours of the game we all are wishfully waiting for. So keep an eye on Diablo-3.net during the 28th and 29th of July when Blizzard’s Worldwide Invitational takes place.
We had to prepare ourselves for the [...]

This is what Diablo3.com reports:
“A rep from Blizzard just sent me notice that there would be no more announcements at BlizzCon tomorrow (Saturday), so for those of you (ie: all of you) who were hoping that this would be the day that Diablo 3 was finally confirmed, I’m sorry to inform you that you’ll have [...]