Blizzard announces worldwide events surrounding the launch of Diablo III on May 15th, as there will be various celebrations of the release beginning the evening of the 14th. This page offers details on all the events, and here's word:

In the US, the official launch event will be hosted by Blizzard and retail partner GameStop at:

    The Great Wheel Court of the Irvine Spectrum Mall
    71 Fortune Drive
    Irvine, CA 92618

Festivities will start at 8:00 p.m. PDT on May 14. Gamers in attendance will enjoy an epic evening of entertainment before Diablo III goes on sale at midnight, including a variety of giveaways; an exciting selection of Diablo-related video footage; and multiple contests with exclusive Diablo III-themed prizes, such as laser-etched desktop PCs from Intel. In addition, members of the Diablo III development team will be on site at each of the official events to meet with players and sign their copies of the game.

For more information on the global launch events, visit http://www.blizzard.com/company/events/d3-opening/. In addition to the official US launch event, other retail locations around the country will open at midnight to support gamers looking to pick up their copy of the game the moment it goes live. Please check with your local retailers for further details.