opml2ft
"opml2ft is a Perl script that converts an OPML document into a JavaScript file suitable for parsing by Marcelino Martins' FolderTree DHTML outliner."

If this folder tree was rendered into a side pane within the browser, that would make user-contributed directories more compelling as far as reading them is concerned. Now comes the more difficult task of organizing bookmarks, one IE consistently mishandled since its early days. I like how Hotlinks supports features such as sort, public/private directories, or drag and drop (see screenshot.)