<link rel="outline" type="text/xml+opml" href="URLOFOPML" title="Name of OPML" />
in a fashion similar to how RSS feeds can be auto-discovered inside web pages by modern browsers (IE7, FF, Safari, etc...). It then provides grazr links for easy viewing.
Grazr already has an autodiscovery mode built in for when it's pointed at non feed or opml resources (like html pages). In these cases it tries to display all the embedded feeds and opml files as a list. When I implemented that feature I'd read several discussions about autodiscovery of OPML but there hadn't been a standard method or link tag agreed upon for opml. (although Tom mentions that Dave has actually specified autodiscovery for OPML, I must have missed it somewhere).
Now that people seem to be coalescing around these new opml link rel's, I'll be adding them to the Grazr autodiscovery mode. The more tools we have for discovering and sharing opml the better!