I've just discovered del.icio.us direc.tor which is an innovative and powerful user interface for managing your del.icio.us bookmarks.
You add a bookmarklet to your FireFox (or MSIE) and launch it when browsing del.icio.us. What you get is a drop-down list of all your tags. Choose a tag and another drop-down list is populated with all related tags. Choose a tag from that ddl and the process continues.
This is an excellent way to find links through tags and to see which of your tags are useful and which are not.