I stumbled upon this video of Kathy Sierra once again today:
She insists on 2 things:
- You need to make your users feel great about what they do and how they do it by gifting them with a superpower
- If you teach people how to become better at what they want to do, they will sell themselves on your product
Once you've done that, they'll become very happy and will talk positively about your company. Once you get people hooked into your system and they can acknowledge its value first-hand, it's much easier to have them pay for your service.
This is also linked to my previous post on single utility in a social system.