Incentives for bookmarking

My Ph.D. student, Rick Wash, together with Emilee Rader, has a new paper on incentives for bookmarking in This paper will be appearing, after some revision, in ASIST 2007, as “Public Bookmarks and Private Benefits: An Analysis of Incentives in Social Computing“.
In this study, based on in-depth field interviews of users, they conclude that

metadata reflecting who bookmarked a webpage better supports information seeking than free-form keyword metadata (tags). We explain this finding by describing differences in the way that the design of motivates users to contribute by providing personal benefits for bookmarking and tagging.

Incentives and tagging (Library Thing vs. Amazon)

Rick Wash pointed me to an interesting blog article about a comparison of book tagging on LibraryThing and on Amazon. The basic fact asserted: tagging is wildly successful on LibraryThing, and has barely had any meaningful usage on Amazon.
The more interesting point for us: why? The author suggests that the incentives are aligned much better at LibraryThing. At some level, that’s tautologically true, but what we might learn from is what the incentives are.
The rather obvious, but important point the author makes (but here in the pithier words of one of the commenters on the post):

people do stuff on the Internet that is useful to them, not out of the desire to make a nifty tagsonomy.

The result may be that a very valuable public good is created (which is true at LibraryThing), but it usually created because the individuals contributing were getting enough value for themselves. This is the compelling logic behind the private provision of public goods.
On LibraryThing, people are cataloguing their own book collections, for their own purpose. Tagging creates organization, that can be used for sorting, reporting, finding. This same motivation is at work on flickr (photos) and (bookmarks).
On Amazon, people are searching to buy books they haven’t read: what gain to them from tagging them? (Some suggest tags can be used to create complex categorized wish lists, but how much value do they add to the flat wish list, when few people realistically keep more than a dozen or two items on their wish list (and tagged structures are not easily viewable by potential gift givers).)
Of course, as striking as this example is, and apparently compelling the logic, it is not so easy to explain all user-contributed content. One obvious relevant example: Why are people spending so much time writing book reviews on Amazon? Surely not primarily to create a set of notes to jog their memory later about what they thought about a book?