I just about get the concept of tagging content on sites such as Flickr. It amazes me that the system doesn't get abused in the same way that website meta tags did in the dark days before Google made our lives worth living. However, it does seem to work so I'm prepared to agree there is value. I guess the incentive structure may be different (i.e. there's no value in driving inappropriate traffic to your images whereas there is a lot of value in driving traffic to an otherwise worthless website that is full of ads, etc).
Taking this a step further, I can see some merit in adding tags to a blog post to let search engines know what it's about. I suppose the likes of del.icio.us may go further in helping *other people* add tags to my content. Fine. Seems like a reasonable idea (although I still don't see how it's protected from abuse).
So the question is: how do I tag my content? Can I tag links that I put into my blog? Or do I need to use some other tool?