Should you make the cut, you'll receive an invitation, which requires a Performance Test. If your settings make the cut (the "cut" being whatever configuration OnLive is looking to test), you'll become part of a Test Group at some unspecified time, at which point the (hopefully) awesome part begins: the part in which you play games. It'll be buggy, and you'll probably have to fill out reports about the experience, but video games.
It may not have been an "official" beta, and it may have been under carefully orchestrated conditions, but our own experience with OnLive was a positive one. We'll see how the public beta compares.