When you go to the del.icio.us home page you’ll see a list of "What’s Hot". This list is generated because del.icio.us can tell when a specific link has been linked by a number of people. Sort of like how Google uses the number of links to a page to help determine if it is useful and relevant, del.icio.us uses the number of links to a site to identify sites of interest in the current moment.
Although this is pretty cool, it’s not the only (nor necessarily the most useful/exciting) way that the social nature of del.icio.us can be used.
Each tag also has its own page. If you were looking for what people are linking to about, say, laptops, you can look at the del.icio.us listing for the "laptop" tag to find out what other people are linking too (or use the model name/number to be more specific – "MacBook" for example). If you use an RSS news reader (like Google Reader), you can also subscribe to a specific tag or del.icio.us user so you can keep track of what’s being added without having to visit the del.icio.us site all the time.
When you add a link to del.icio.us you may also see that it’s linked to by other people. If you click on the "saved by X other people" link next to your bookmark, you can browse what those other people have linked to.
Additionally, if you tag something using the "for:<username>" syntax, that will appear in the "links for you" section of that particular user’s del.icio.us profile (you can see this as a link at the top of your del.icio.us profile page after you have signed in). For example, my del.icio.us username is "grantyoung" – so tagging something as "for:grantyoung" will appear in my "links for you" section. This is a great way to share bookmarks with colleagues or friends. Sending a link this way means that only the "grantyoung" user (me) will have access to the link.
As you can see, there are many ways that the collective value of using del.icio.us’ bookmarks emerges – all from individuals saving their own pages for future reference.