Two weeks ago, Gayardos, the admin of the Spanish Diablo 3 blog - diabloiii.es, reported that he received a certified mail from a law firm by order of Blizzard in which he is told to give up this domain, to redirect it or to transfer it to Blizzard.
He seems to have no real chance to keep the domain, as he wrote in a longer blog post today.

It is not the first time that Blizzard claims a domain which includes parts of registered trademarks of Blizzard Entertainment and it won’t be the last time. But that they took action at this point in time, close to upcoming WWI 08, is very remarkably. It could be another hint for an announcement of Diablo 3 in the near future.

//edit

Blizzard is now the official owner of the domain diabloiii.es.