It's largely random. We do our best to make sure we have a good mix of players. I've seen it before where one friend has posted on the forum about another friend who got in but they didn't and why didn't they when their friend is the one that only plays casually and they (the op) are the one that is hardcore. We're not looking to pick one demographic to help do the testing. We look for a good mixture of people with different play styles and interests. It gives a decent snapshot of what issues need fixed or tweaked prior to release.

The random beta tickets are sent out by email. It's why when it comes time for a beta, we will remind everyone (sometimes to the point of annoyance) to please please please update your contact information and email. There were many people that never got an invitation because they had a bad email.