WWDC tickets went on sale today, and the event sold out within minutes. This year, Apple developers were prepared to buy their tickets as the company pre-announced the ticket sales one day in advance. In previous years, the conference was announced and tickets went on sale at the same time.
If you didn't get a ticket this year, Apple is streaming the video from the sessions during the event. You won't get the full experience of being at the conference, but you will get a lot of the important parts. WWDC 2013 will be held from June 10 to 14 in San Francisco.