http://www.tentonhammer.com/node/67008

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Vogel: We feel that limiting the [number of] beta testers is a good thing. We get better data with fewer, more dedicated players and we are able to focus test specific areas of the game. You cant do that with tens of thousands of players. It is a coordination issue. It is good, however, to allow enough players into the game to make sure it can handle the load under stress.

About 4 weeks before launch is a good time to open the game up to consumers. If you have done your job right, you will know if the game is ready before you open beta. If not, you dont open it until it is. It doesnt hurt a company at all to open the game up to players four weeks before launch. It allows them to try before they buy and it allows us to make sure the game holds under pressure as well as providing a rolling launch so day one is not so crowded.