"(...) tagging system is not "controlled" in this sense (...), but I'm wondering whether its web-scale nature can provide some benefit that one would not expect."
"(...) has the most power and value in vertical search-style app.s, where a community of experts contributes to a pool of content that is then rated by other experts, assuring that the best available content is recognized and becomes readily available."
TagCloud is an automated Folksonomy tool. Essentially, TagCloud searches any number of RSS feeds you specify, extracts keywords from the content and lists them according to prevalence within the RSS feeds.
B. Krause, R. Jäschke, A. Hotho, und G. Stumme. HT '08: Proceedings of the Nineteenth ACM Conference on Hypertext and Hypermedia, Seite 157-166. New York, NY, USA, ACM, (2008)