Did you get an email inviting you to tell Valve more about yourself? If you had previously signed up as being interested in the Dota 2 beta, you probably did. Those who fill out the survey may get an invite when the next wave gets sent out.
Perhaps best of all, every beta invite comes with two more that can be gifted to friends. Let's face it, not everyone is obsessively into playing MOBA games competitively, so this is terrific news. And, in typical Valve fashion, there's a comic for us to peruse.