Web applications such as Facebook, Wikipedia, Digg, Twitter etc. clearly thrive on user generated content. Let's sidestep the issue of actually monetizing these for this post. And look instead at what drives the ecosystem. There appear to be 5 Cs in motion. Consume, Communicate, Comment, Convey, Create. And these are actions users take in these applications in increasing order of difficulty/time consumption. I believe there is one C missing (if you haven't gotten a hint from the title) and that is to Collaborate.
Most users obviously consume information. At least one web search a day of mine goes into Wikipedia. I read and exit the website. On Facebook, I consume my friends' pictures, status updates, whereabouts etc. This is the easiest at the same time the most valuable per time spent.
Quite a few users communicate on these sites. We write on friends walls, we send each other messages and we setup event pages. In Twitter, we communicate our state at the moment. This is one where the fruit of the action is not realized until/unless someone reads our communication and/or takes action. Communication is a basic need of a social being and thereby is a common action.
Commenting takes time, takes thought and takes courage. I'll get to why it takes courage in just a second. We comment on friend's status updates, posted items, photos. We comment on Flickr photos. We comment on blog posts. Commenting takes time and takes thought. To comment usually means to have consumed, understood and created opinion. And to state one's opinion publicly takes courage.
One way of defining Conveying in this context - To take information from one point and paraphrase (or not) into a different context. We post news article links/video links/opinion links on Facebook. We Digg links we like, thereby conveying information to a different audience. Conveying happens after consumption, but requires the almost extraordinary step of wanting to share. Now, there can be several reasons to share (excitement, breaking news, altruism, known external interest, attention wanting, spamming prone). But the prerequisite is to have consumed information outside the medium we are posting in. And this takes a lot of effort and time.
Creating is no doubt the most difficult, time consuming of these all. We create notes on Facebook. Developers creat applications for Facebook. Developers create Twitter apps. Wikipedia contributors create/edit articles for free. Wikipedia moderators keep the noise out. Creation is several levels more difficult than even conveying as it requires original thought (in most cases) and the creative ability to put it in a consumable form. Also, by creating a user displays extraordinary courage and conviction in their work and is open to criticism.
I believe there is a 6th C that is yet untapped in all of these. That is to collaborate. Wikipedia taps it to a certain extent as users can edit others posts. But think of the possibilities here! Think of Facebook users coming together to collaborate on a thesis/invention. Think of Twitter users coming together to collaborate on raising money for the poor. Imagine if in Digg, I could customize my news stories to only include Diggs from certain clans of users who form through an overlaid social network. Imagine Orkut users in a certain neighborhood coming together to setup a neighborhood watch. All of these are not impossible. But they need a collaboration engine to be created that has incentives for such activities to take place. An analogy - Wikipedia created an engine to let creation and moderation be a breeze. Facebook created an engine to let online application development and usage a breeze. Now, can we create an engine that makes instant, productive (1+1 > 2) and results driven collaboration possible?