Social bookmarking (eg. Del.icio.us) is one example of social tagging. IBM’s internal Fringe application (also called Bluepages+1) is another example that goes beyond social bookmarking to tag people rather than web pages. In this author’s opinion social tagging is the most valuable feature of a corporate whitepages.
Social tagging is merely the ability for multiple people to describe a single object with free-form words. It is far superior to author/creator tagging because it allows those who are making use of the item to be the ones who are describing it. Thus, the descriptors are likely to match the way that the target audience perceives the item and its value.
I will leave the discussion of free-form tagging vs. structured hierarchical taxonomies to another post, but having created structured taxonomies for multiple businesses in the past, I know there are many difficulties/drawbacks to doing so. Tagging is much more organic and scalable though it does have some drawbacks.
One of the most difficult elements of creator only tagging is that the incentive to tag is purely altruistic (good of the firm) or recognition based (I want people to find this so they know I am the expert). Social tagging introduces an additional incentive. In tagging something/someone, I am creating a breadcrumb back to that item. At any time I can recall the items I have tagged with a particular word. Also, not only am I creating a better sense of the item I am tagging, but my tagging act is helping to describe me. A view of my tagging words helps to understand me in the same way that perusing the bookshelf in my home would.
Even the number of tags on an item tells us something about that item. An item with more tags may be more popular. We have to be careful with this until social tagging is mainstream because there will be a skew towards the naval gazing of web2.0 type topics.
As with anything the social tagging user interface is ever important. If it is cumbersome to enter tags, users will not do so. The Fringe example from above was ideal because one generally looked up another user for their phone number and then while you were chatting to them could multi-task to attach some tags to them about the topic being discussed.
One of the most important factors in social tagging is the long tail. While many people will not social tag, there will be enough people in the long tail who derive personal and altruistic value from the act of tagging that they will tag a large portion of the items in order that the masses can better search.