Clay Shirky answers a question posed by Tim Bray: “re there any questions you want to ask, or jobs you want to do, where tags are part of the solution, and clearly work better than old-fashioned search?”
First, tags keep found things found. Search is about finding things, tags (in the del.icio.us mode) are about keeping them. Like many people, I stopped remembering things when the internets came along, and started remembering pointers to things instead. Manys the time Ive wanted to find something I read N months ago, and had to remember whether I saw it on slashboing or blogpop, or I had to recreate a multi-word search on Google. Tags, fby contrast, are thumbtacks with filters.
Second, tags add people and time as cross-cutting elements. del.icio.us provides a measure of social velocity I have not worked in a development shop for some years, and would have missed the significance of the original Ajax article, but seeing the ferocity of attention on del.icio.us, I knew that something important was going on, not from reading the article, but from reading the userbase. Again, you can imagine adding this sort of thing to search, but youd do it by watching what people tagged.
Third, a look at the top tags on del.icio.us reveals several that could not work as part of a search. I cannot search directly for things toread, or things that are fun, funny, or cool, because those are in the eye of the beholder. I cant search directly for tools or reference, because what I consider a tool or a reference work is different from what you do, and people writing things that I might think of as a tool or a reference work rarely label them that way.