I first became acquainted with tags somewhat in the reverse way that the 23 things on a stick recommends it. One time I decided to upload a video on YouTube. When I finally manage to successfully upload it, it asked me to tag my video. At first I did not know what they were talking about. Then I realized that YouTube was asking me to highlight the words that would link a user to my video. It was basically telling me to define the subject of my video using the most representative words, not sentences, not paragraphs, single words. The idea, I understood at the time, was to imagine that other people were searching for information that I thought my video was part of. If I wanted my video to be found by other people, I had to imagine people entering information on their browser that would describe my video. Whith this in mind, I chose the single words that I thought those looking for the information in my video would type. Choosing single words that would describe the subject of my video was very hard, but carefully chosen words or tags can mean success or failure in the Internet environment.
Just now, I signed up for a del.icio.us account. I believe that, even on the early days of the Internet, many people though it would be a pretty good idea to be able to categorize their favorite website using terms, or tags, individual to them that would tell them what a website was about, instead of memorizing URL's that made little or no sense to the user. A URL gives very little information about what a website is, but if the user defined him/herself what a website was about, based on his or her own perception, and could categorize a collection of sites based on the user's perception of a website, it would simplify bookmarking. Del.icio.us does just that.