To every modern web 2.0 site offering tagging seems to be an absolute requirement. While I may agree, that tagging in some cases may offer some improvements in content navigation over many other points, I do think it’s been too abused in way to may cases.
Tags on sites such as Flickr and Del.icio.us are absolutely fantastic. They offer some cross navigation options, which would probably be near impossible, if not for the tags. I often find my self exploring links though del.icio.us, since the content stored there generally seem to be of a muh high quality than a simple Google search on a common term.
The newest WordPress Release (version 2.3 ) supports tags right out of the box, and I’m sure those not using tags already will go crazy with them, and most wordpress installations will feature tag-clouds within a few months. I’m also sure, that most of these tag clouds shouldn’t be tags, but categories.
Now the problem with tags in most cases, however, is that often there’s only one piece of content per tag (or at least very few). This to me suggests that it’s too easy to make tags or that the author/publisher doesn’t know how to use them. Tags are great for making collections or making ”cross-user navigation”, but if you’re the only user publishing in the tag collection or you doesn’t have content to have a number of posts per tag, then you’re probably better of using categories.
That’s my $0.02 for the time being anyway..