OPML packages data so the possibilities are endless…I remember a while ago coming across a bookmarklet, that would generate a list of hyperlinks contained on the web page you are viewing.
This packaged in OPML would be great, if this was a blog essay, it would be a start to making a bibliography in an outliner…you could include the link to the blog post as the first item, and the rest of the items is the bibliography. People could include this OPML in their own, they could read it in an OPML Browser, they could take bits from it when making their own outline, they could convert it to HTML.
You could send the outline to someone as an OPML URL where they could import it into their OPML editor or they could save it as a local file and import into the OPML editor, from here it would be great to say send this to word, excel, or powerpoint.
Another use would be to import all these links into a bookmark manager (if it accepts OPML), or get a search engine to search the full-text of these links in the OPML URL, by just entering the OPML URL in the search engine along with a search term.
[ADDED 10/04/06: here it is]