Facebook now requires us to shell out money in order to get users to like our page, and they also require us to pay to reach these same users. This is insane. What's the best social network for startups? One that would allow minimal payment, and yet has the viral factor enough to compel us into fame?
I've loved Reddit.com from a viral / incoming traffic point of view, but you've got to be a broad contributor, ensuring that you post non-business content and interact on other's contributions. If you only self-promote, you'll quickly get banned from the "sub-reedits" you really want to post to.
It helps to make sure your customers and friends know when you post on reddit. Organic "up votes" can take your links from getting a few hundred hits to 10,000+.
Hope that helps!
Coach, consultant, and therapist to entrepreneurs