I first encountered effective end-user tagging over a decade ago in a bookmarking program named PowerMarks (no longer developed).
It would ("instantaneously") generate an automatic set of tags based on page content and metadata. This could very rapidly edited in the form of a simple, comma-separated list of text.
Bookmark search consisted of typing in a simple, comma-separated list (IIRC). The current contents were continuously parsed and partial matching performed to produce a ranked list of matching entries. With thousands of bookmarks, the desired entry could usually be identified and followed within a second or three.
(There were also date fields and some other fields, that could help in clustering and could be used in ranking)
The combination of a tagging categorization, and the very efficient interface, made it a joy to use and extremely useful.
This thread's product appears, from the video, to be moving the interface portion of web-based tagging in what for me would be a "right" (correct) direction. Make the tagging rapid, and the interface painless, and perhaps tagging will really take off as an end-user interface.
Note: I followed vijaydev's link, as the ur-parent's link is currently unresponsive.
I suppose using this for tagging stuff has two positive side effects:
1) You can now use longer tags, with whitespace, capitalization, etc.
2) Duplication of tags is much smaller.
Kudos to the author.