I'm not sure if this goes in this thread, but you should keep track of referrals a certain profile gets. Like have a link that when people sign up using the link, 1 referral goes to whoever gave the person the link. I know that would make me try a bit harder at getting people to sign up and download. 
I also have a lot of forum buddy which I could bribe into signing up, like 'I give you a referral if you give me one...' I'm sure I could get a couple to 'sign up' getting them to stay is a different story. Should I try to get people to sign up? Even if it's just a bribe or something?
Added (11/05/2010, 05:01)
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If you ever do the intro, make sure it's skip-able for people who have a slow connection.
