I continue to be fascinated by everyone's determination to wrap user-created content into their new web services, despite their flamboyant display of ignorance as to *why* users actually create content. Here are three distinct models that can help you think about why users create:
1) Selfish UCC. Delicious bookmarks and Flickr photos. I primarily bookmark and take pictures for myself -- because I want to remember, or because I like something. I use these web-based apps instead of client-side equivalents because I personally get more value out of them. While the social benefit is apparent, I view that social benefit strictly through a selfish lens -- instead of emailing pictures to my Mom, I can just point her at Flickr. I encourage other people to use these sites for selfish reasons as well -- it makes it easier for me to keep track of their UCC. Another great example of selfish UCC is every auction on eBay. Those sellers are not putting those auctions up there to help anyone but themselves - any general benefit is strictly a secondary effect. It's not necessary for any individual item of UCC to relate to any other item - a picture or a bookmark has its own stand-alone value.
2) Social UCC. Blogs, Slashdot comments, and Yahoo Groups are great examples. People create content in order to express a point of view within a larger conversational context. There is usually an implied audience and an implied reference in most of this type of content. Why do people create conversations? It's somewhere between selfish and selfless - call it social. We want to take part in something larger than just ourselves, but we expect to benefit as well. In this case, personal and general benefit are deeply intertwined, and each item of UCC relates to other items of UCC.
3) Selfless UCC. This is the one that leads most everyone astray. The single great example of selfless UCC is Wikipedia. If I am an expert in subject X, I already know all about it. I do not benefit personally from writing down that information and sharing it with the world -- I am primarily doing it so that you, the reader, can benefit; or out of some sense of "greater good" and contribution to something shared and larger than just myself. It's a very noble aspiration that drives this kind of UCC, and it's not particuarly surprising that this makes it the most rare. Implied for this sort of content is a weak sense of authorship -- if I am personally attached to the content, it begins to look much more like a conversation.
The obvious non-UCC example of this strong authorship point is newspaper reporters vs. columnists - a column is a conversation, whereas a byline is subsumed (largely) by the headline and content of the article.
There are particular issues inherent to each different type of UCC:
1) For selfish UCC, the issue is relevance and commensurability. If I take notes on something for my own purposes, there's no reason for me to care whether it accords with anyone else's notation in any sort of commensurable way. Delicious tries to address this problem by suggesting tags that other people used on an item; this drives convergence on certain terms, making their programmatic understanding of what that item is more robust.
2) For social UCC, the issue is personal opinion over-riding fact. Every conversation implies ego and point of view, and in reading a conversational thread, one has to constantly be asking "what was their motivation in saying that". Bias is inherent to the medium.
3) For selfless UCC, the issue is quality. As people are endlessly pointing out, there is a lot of crap in Wikipedia. You may not agree with someone's opinion on Slashdot, and you may not find my bookmarks in Delicious useful, but there are strong incentives in both contexts for me to at least try to make my content accurate. In the selfless context, well, the incentives aren't just as strong.
This suggests obvious remedies in product design:
1) For selfish UCC, take note of Delicious' example and try to drive general relevance without interrupting the selfishness of your users. Delicious prompts me with terms others have used, making my selfish life easier while making relevance of my actions more general.
2) For social UCC, create programmatic mechanisms (like polls or votes or star ratings) that allow people to quantify their point of view on some abstract scale. This will benefit the user (by allowing them to say simply, "I am *very* Republican," for instance) and benefit everyone else -- who can then say, "He's *very* Republican, and I can easily assess where he's coming from."
3) For Selfless UCC, use human editors to manage quality, and try as much as possible to create "superuser" editors to do this for you. The cost-benefit ratio is outstanding, so get over the stone-ageness of it and go make money.
If you apply this model to a lot of the "Web 2.0" websites out there, it readily explains why there are such issues with the user-created content on most of them. UCC is a two-edged sword, and must be used well to avoid injury.
Note on terminology: I deeply dislike the term "User-Generated Content" (UGC). People don't generate (a mechanistic or animalistic term), they create. Creation is a deeply human act, and we should celebrate it.
Update: Find more at the follow-up post "Market Goods, Cavemen, Schadenfreude"