From what I've seen, del.icio.us, et al is like the bookmarks in your browser where you can save websites, urls to online articles, etc, but this time your bookmarks reside in del.icio.us server so that you can access it online from any PC.
del.icio.us lets you share your bookmarks to the public, to restricted individuals, or simply keep it private for your own personal use.
What I haven't quite figured out is how to use social bookmarkings for website promotion.
Renato
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