The discussion of what makes something truly "social" - and how to do this, seems pretty set by the web community. Hollywood is getting on board - for the more mainstream or younger-demo focused films and more.
These points are important to keep in mind from a ohHeyWe'reMarketingOurShow perspective:
1. Think Content, Not Ads
2. Mix It Up
3. Look for Social Distribution
4. Use Social Analytics to Test Content
Of course, the question of how to get people to share isn't always science. Some things that should really not get shared (Charlie Bit My Finger, anyone?) and stuff that seems perfectly set to go viral... doesn't.
It's a mix of authenticity with innovation. Fun mixed with uniqueness. It's got that je ne sais quois that makes things interesting.
And the one thing that makes the Internet interesting is that you can change things on the fly (not easily per se, but it can be done), so if a trailer or teaser isn't working for you there's an ability to try again. To find something that will or can be shared more easily. Innovation and fun. Uniqueness and humour. And - most importantly - getting in touch with people to share things.
After all - the Youtube metrics have changed - and there's 48 hours of content uploaded every second.
The signal to noise ration is getting worse. So you have to find people to champion your project.