The Pew Internet and American Life Project has just released a report on Tagging with some very interesting statistics (”28% of internet users have tagged or categorized content online such as photos, news stories or blog posts. On a typical day online, 7% of internet users say they tag or categorize online content.”)  There’s also an interview with Tagsonomy blogger David Weinberger:

Q: Why do you think Internet users are drawn to tagging?

Weinberger: It’s really useful. Compare your traditional computer system to organize your digital photos to using a tagging system. Instead of having to stick a photo into a single folder — say, “trips 2006” — you can easily tag it as “Italy,” “anniversary,” “sunset,” “mountains,” and “no kids.” You can assemble instant virtual albums of all your anniversary photos, or all your photos of all your trips to Italy, etc.

There’s an altruistic appeal to tagging as well. Tagging at public sites can give you a sense that you’re adding to a shared stream of knowledge. At del.icio.us, or other such sites, tag a page “robotics” and you know that it’s automatically added to the list of pages tagged that way, so anyone else interested in that topic can find it.