An old fansite for the Diablo series, Diablo3.com has had a countdown for a few weeks, to something that "half the internet will be linking to." It may not be May 1st, but sure enough, the announcement has been made.
According to the new location of the site http://www.diablofans.com/, there were contacted a few months ago by Blizzard about the domain name, and sure enough it was bought out. They said not to consider it as an official announcement.
Hmm, really? Seems close enough for me. Diablo 3 seems all the more possible