NET - Passado uses a game to quickly grow

I have just received an email from Passado: it seems like they want to quickly grow their number of members. They give the chance to win a digital camera.

Viral marketing
They ask their members to spread the word, and send an invitation to 5 of their contacts. It is a quite common example of buzz & viral marketing, but it is the first time I see such initiative from a social network. Do they plan to sell soon?
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Technorati: socialnetworking, passado, marketing, buzz