chriscrutch, I am putting together a screencast of my use of EverNote. You will see soon how I envision DOpus to work, based on my use of EverNote.
As for flat vs. hierarchical tags, I believe that hierarchy gives more flexibility and another dimension to tags. I am certainly not a disliker of hierarchies (although I realize I may have made it sound that way). What I do dislike is not having a choice for the right tool for the job. Hierarchies certainly have their place and usefulness, and with hierarchical tags I feel that we get the best of both worlds. Again, you will see this in my forthcoming screencast of EverNote.
Just to give you two quick examples, one "right" and one "wrong":
-Philosophy
--Greek
--Eastern
This hierarchy example, in my classification cosmotheory, is wrong. Why? Because "Greek" is a much more general tag than this implies. This hierarchy implies that for something to be "Greek", it has to be about "Philosophy", which is clearly wrong. "Greek" is a much more broad concept that involves (and has to do with) a lot more than Philosophy.
Another example:
-Programming
--C++
--Visual Basic
--Delphi
Now, I feel this is about right. For something to be about "C++", it has to be about programming. It cannot be about something else. This way, I could choose to browse about ALL programming related stuff, not just C++. I couldn't do that with non-hierarchical tags (unless I also tagged everything with "Programming" as well, which cognitively is a lot of work, and I will, more likely than not, forget to do it).
Of course, I would also tag it as something else, for example:
What is it?
--Sample code
--How-to/Tutorial
--Opinion
--Analysis
--Article
So, yes, something is about "C++", but what exactly is it? It could be actual sample code, it could be a tutorial, or it could be an article about the usage of "C++" in the marketplace.
So, in a nutshell, the more tags you give to an item, the more "dimensions" you introduce to it, and to the ways you can browse for it. So, I believe that hierarchical tags eliminate the need for giving a whole lot of tags (which is messy and a lot of work), and help organize many concepts together. This leads also to good, logical organization of tags that make logical sense. It cleans up, tidies and organizes your tag landscape, so to speak.
Last but not least (and this may be the most important point here), without hierarchical tags, you CAN'T HAVE faceted classification!
More later.
Cheers,
-ilias.