Though I didn't get in last night in the first round of Twitter contest invites, I do know that they are sending emails to the winners. A lot of people emailed in their entry on accounts that aren't tied to their battle.net email, so it gave them a little grief to notify and verify the winners.
EDIT- I was partially wrong- They are sending notifications via the direct message within Twitter, but they really want your email address tagged with Twitter to match the one linked to battle.net.
4. Contest Rules and Prize. Each Tuesday during the Contest Period, Sponsor shall randomly draw One Hundred qualified entrants who will receive one (1) Diablo III Beta Test Key. All Contest winners will be notified via Twitter.com’s “direct message” system with instructions for claiming their respective prizes. Prizes that remain unclaimed thirty (30) days after notification will be forfeited.