I dont know if you measure such thing but why not to pick players (real fans) that?
1- Registered all your games in their accounts.
2- Have a big number of posts on the old forums.
3- Have a large number of posts on the new forums.
4- Login on their accounts every single day looking for a beta key.
5- Bought a virtual ticket to Blizzcon 2011 and 2010.
6- Was a Beta tester in the past and reported a big number of bugs instead of just ignoring it?
That would be fair to the real fans. I see so many beta testers asking questions that shows they never got interested on D3 before playing it that makes me sick.
Bashiok please consider this post and talk to the team