The Counter-Strike: Global Offensive team just published a blog update detailing how future sets of beta keys for the game will be sent out. Key recipients will be selected from a pool of people that've completed a survey. The survey is a simple template intended to judge your CS savviness, combined with an automated peek at your hardware. Copy this into a Windows Explorer address bar to open Steam and start the survey: steam://takesurvey/2/
Being absolutely honest about your skill, as I have above, is probably in your interest. "Over the coming months we will make selections from the survey participants. Sometimes we might add experienced players, other times new players. Sometimes 1.6 players, sometimes CSS players, sometimes people who have played neither."
"If you don't fill it out, you won't be getting a key," reads the post. Of course, Valve also states that active, current CS:GO players can expect to receive keys to gift to their friends through Steam.