Rated 3 out of 5 stars
I like the concept of tags, but I think this could be tweaked just a tad...
One way to tweak this particular extension would be to add topic-specific sub-tags beyond folder and subfolder names.
For instance, say you have a folder-tag name called "Research sites" and a subfolder called "science" and another called "spirituality." If you wanted to cross-bookmark a site that concerns BOTH subtopics, you'd want to be able to add tags that encompass both those subtopics and therefore automatically place the one site in two different folders within the main "Research" folder.
This is just one example of how *I* would want to use Bookmark tags.
Other than the desire to cross-bookmark/tag sites (like one cross-tags blog posts), I like this extension...the Tag Icons are cute, at least. ;-)
Oh, one more thing.
Would there be any way to tweak the code to make color customization WYSIWYG-style, so that those who have no clue about how to use CSS (and don't have much desire or time to learn) could customize their bookmarks without having to muck about with the code? If you could do that, I'd give this a four instead of a three.