Blizzard teases us so? Well, it could mean many things. This very type of teaser has been used for several other announcements in the past, so your guess is as good as ours. If we had to wager an educated guess, we would say that a closed beta start date and release date is about to be announced for Wrath of the Lich King coinciding with the Blizzard Worldwide Invitational. Although we'd also love to think that Blizzard was close to announcing their next MMO, but that probably won't happen for a very long time.
Then again, as far as we know Blizzard has never teased us about a release date. So if you want to start making your wild guesses now, that piece of information is a good place to start. If it's not WotLK-related, our second guess would be an announcement that Diablo 3 is being "thawed out" for everyone in the near future. Yeah, we know it's a (lame) stretch -- but that's half the fun of it!
Update: After some poking around, we've discovered something interesting. Out of all the Blizzard websites, diablo.com is the only one that points our browsers to this splash page. Simple coincidence or subtle hint? We'll let you guys be the judge.
Update 2: Apparently diablo.com has pointed to blizzard.com for a while now. It looks like simple coincidence is much more likely in this scenario.