See a set of links recently added to del.icio.us.
When you log in to del.icio.us, you have access to a "post" form that can be used to add any URL of your choice to your personal list of bookmarks. del.icio.us also provides a Javascript widget that you can add to your browser's tool bar to easily add the URL of any page you are viewing to your collection of del.icio.us bookmarks. You have to provide a descriptive title for each link you add; if you use the provided Javascript widget, del.icio.us fills in the description field for you based on the title of the page you are viewing. You can also provide a list of keywords for each link and use these tags to organize your bookmarks in del.icio.us.
You can use the keyword tags added by other del.icio.us users to their collections of bookmarks to search for links that might be of interest to you. You can also view the list of bookmarks entered by any other del.icio.us user.
del.icio.us provides a variety of RSS feeds, enabling you to subscribe to your own list of bookmarks, all bookmarks having a particular keyword tag or all bookmarks entered by a specific user.
Brief Educause article "7 Things You Should Know About...Social Bookmarking"
Instructions for installing del.icio.us as your main bookmarking tool in Firefox
Video explaining social bookmarking in plain English