In a now-famous article for Feed Magazine, Mark Pesce sounded a warning bell about XML.
As you have seen, there are many ways to decide how to tag content.
If every user does his or her own thing, we will lose the potential for interoperability between documents.
Pesce referred to this situation as the "balkanization" of the Web, and said that we would be in a sort of tag gumbo, with no way to discern valuable content. Others have argued that we are already in tag gumbo, and that without a new standard for defining content, the Web will continue to present billions of words but little intelligent data. The freedom to create tags is also the freedom to create chaos.
Fortunately, standardized industry vocabularies are being created, one of which is the Resource Description Framework, which will define the sets of tags we may ultimately use. Rather than continuing to reinvent the wheel, you are encouraged to seek out and pursue emerging industry languages created from XML.

The growing balkanization of the web is the worst enemy of the internet. As worldwide literacy grows exponentially on the web, such expansion results in increasing pressure from corporate interests and regulatory agencies. The net has become a symbol of borderless communication between individuals and of unlimited access to knowledge. The internet is about to become a heavily controlled environment, serving two classes of citizens: a dominant class that sets the rules (technological, legal and commercial) and the subclass of citizens and consumers.