del.icio.us

del.icio.us is a really interesting web service that lets anyone who uses it "tag the internet".

Simply put, tagging is the exercise of associating words, any words you want to use, with URLs. That's all it is - a series of words and URLs. The words are the tags. But when lots of people start tagging with a similar tool and similar words, and the tags are shared, some very interesting things result. RSS feeds make tagging even more powerful. Because everyone's tag can be an RSS feed, tagging becomes extremely viral and portable.

Jeff Jarvis was the first person that pointed the power of this out to me.  I asked him about del.icio.us and he said that he didn't tag, but he pointed me to this tag that he subscribed to as an RSS feed.  It was like looking at someone's personal daily bookmarks.  That was the aha moment for me.