You might have a web browser that allows the user to assign pseudonyms to websites. A user could have the word "news" mapped to "news.ycombinator.com" for his browser. If such a browser collected pseudonyms from enough people, then the pseudonyms applied to each site could start to have importance and make it easy to give an intelligent guess on what the user might want. I guess the idea is to apply del.icio.us type information to the url bar.