A national study out of SDSU shows that 57% of young people believe their generation uses social networking sites for self-promotion, narcissism and attention seeking. This is important for you as a product developer/designer because this emotional-need forms the basis for creating virality in your products. People don’t just share messages to be nice to their friends. Take a look at Facebook or Twitter, for instance – often status messages are equally about saying something about the sender, so the important question you should ask yourself is: "How will the message I want spread make my audience look cool or clever to their friends, colleagues or customers?"A few examples:

1. Make them show they are early adopters. Make users feel important by giving them something to say about themselves, e.g. I am a user of this new cool software – it's still in closed beta – but I can try to get you an invite.
2. Make them seem funny or interesting. When adding a  'tell/invite a friend' into your sign-up flow be sure to spend extra time making your invite email interesting. You are essentially the ghost-writer for your users. Make them sound funny or interesting – they will want to share your story with more people.
3. Allow people to add their personal touch to your story. Users are more likely to spread stories that have their own personal touch. So leave room for them to add their fingerprint to your narrative easily. I guess my best example is to always allow for a bit of space when you do tweets – so people can add their own comment to your narrative. By doing that, you allow your audience to become co-senders. If that fails, then piggyback your message on to something entertaining, as a last resort, in case there is no other way to make the message itself cool to communicate. Just think of how OfficeMax have made you Elfyourself.com
4. Make people better storytellers by giving them templates or 'guide them'. Facebook’s initial status update did this delicately by adding the ‘Henrik is…’ to each update. This forced users to write a certain type of update and allowed them to be more creative by working within the template of the 'Henrik is...' template. A new trend is to give people personal information about themselves to share via Behaviour Generated Content generation.

Any other examples?@werdelin