In Hesham Allam’s article “Social Tagging as a Knowledge and Discovery Tool”, he discusses the benefits and drawbacks of social tagging as an alternative to indexing web-based content. He highlights many worthwhile reasons to use social tagging, the most important of which, I think, is the ability of social tagging to provide current keywords. For example, new terms are being created every day to describe technology, concepts and events. Because of their newness, they are not likely to make it into a thesaurus or in the Library of Congress Subject Headings any time soon. By having the ability to assign keywords relevant to these new terms, web searchers can locate related materials in an easier manner.
On the flip side, however, the role of the professional cataloger or indexer should not be discarded. Thesauri have been created for a reason and they cannot be entirely replaced with a set of user-provided keywords. Perhaps the best of all worlds includes a system where a combination of thesaurus terms and social tags can live in harmony.
This is an interesting thought about tagging to use for ways to find information. However, unless the word (tag) is contained within the article, the entire document is ususally indexed and can be found any way with the tag or what you call keyword which is hopefully already embedded in the document.