I don't know, I posted this to generate a discussion.

Thinking logicaly there has to be something to it - if a given person is exceited to level X he will call his friends and tell them about it. If he excited to level of 0.75 X he may send them an email. What if he is excited to 0.1 X? How can we make a good use of that person's modest excitement?

If you writing a twitter app this is relatively easy - nudge the user to twit to all their friends about that particular app. The barrier is very low in this case.

If you are writing a facebok app you can also use pre-canned social graph.

But what if e.g. you are writing an iPhone app? What can you do to convince people on a given level of excitement to talk about your app with others?

They don't entice me to share. OTOH, when I have the impulse to share something, I'm much more likely to do it if it is easy to do, especially via apps I already use regularly.

Yes. YouTube only had 150 videos uploaded after their first 1.5 years of existence. But once they added the click to share buttons and allowed users to embed their content they went crazy viral.

On Domino's pizza tracker for online ordering, you can now "share it on facebook" with a button. I'm surprised at how popular that thing is.. and it definitely social proofs domino's and leads to viral behavior patterning