Folksonomy vs. architecture

We have been mulling over whether the traditional nav bar architecture is a dying breed. With the forthcoming ubiquity of Tag Clouds - is it really necessary to categorize information?

I would argue that in the case of content sites, architecture and search are still vital components, where the information can, in fact, be categorized. But in the case of flickr or YouTube, where architecture is nearly impossible, Tag Clouds - and search, of course - are the only way to go. YouTube does, in fact, have a nav bar, but I find it relatively useless. Now that I think about it, when tagging is such a prominent feature of their site, where is their tag cloud? Hey!