Here is the most general thoughts I have on the subject: If your site NEEDS users to get users, you need a soft launch where you do whatever you can to get use

Here is the most general thoughts I have on the subject: If your site NEEDS users to get users, you need a soft launch where you do whatever you can to get users in and keep them, then you have a bigger launch where you can say "Look what we've done with only x users! This is going to be great!" If your site doesn't need users, then grow organically, 5 or 10 at a time, and work towards an exponential curve.