If you have a large library with hundreds of tags, the alphabetical list of tags becomes a bit unwieldy. Wouldn't it be nice to be able to organize tags the way one organizes folders, ie, in collapsible hierarchies?

Let's say your research involves a comparison of Africa and Asia. So you create the tags "Africa" and "Asia", and then within those you create subtags for various African and Asian countries. Then, you could create further more specific subtags within those country-specific subtags. It starts to look a little like a traditional hierarchical folder system, but the big difference is that you can assign any number of tags to a given item (that, in my view, is the glory of tags). When you want to just focus on Asia, you collapse the parent tag "Africa" so that all of its subtags disappear.

Ideally, there would also be an option such that once an item is tagged "India", it automatically gets the parent tag "Asia" as well. That way, an artical about India would appear whether you click on the "Asia" tag or the "India" tag.

(Of course, users wanting a traditional list of tags would be able to go on using them without problem -- subtags would simply be an additional option.)

In general, there has been a shift over the last several years from folder-based organization to tag-based organization. Now some developers are moving toward hierarchical tagging as the best of both worlds -- a couple examples are Aperture and Things for Mac. (To be clear, hierarchical tagging would not take the place of Zotero's "collections"; rather, tagging and collections would continue to co-exist.)

(I posted a related comment here:)
http://forums.zotero.org/discussion/700/equivalence-of-collections-and-tags/#Item_14

Thanks