The lottery situation with Google I/O this year means nobody is guaranteed entry. Google knows this. And it's Google we're talking about. So they planted a bunch of secret codes you can redeem for a guaranteed I/O ticket. The hunt is already on, and some lucky folks have already won.
Correction: You don't win free tickets, but rather a guaranteed opportunity to buy them.
Good scavenger hunts are tough, and the best ones don't even announce the rules.