It's not about the format, it's about what being in someone's OPML file means. It means that someone finds the information from a specific site to be so useful

It's not about the format, it's about what being in someone's OPML file means. It means that someone finds the information from a specific site to be so useful that they want to receive every update from the site so they can at least take a glance at it. Votes on specific links are a far less valuable indicator of reputation. No one wants to see everything that's submitted to Scribd; a few things just happen to get voted to the top of social networking sites because they're funny or interesting. That doesn't say anything meaningful about Scribd's reputation. Google has a huge advantage in this area since they collect which items from an RSS feed people actually read on Google Reader. They know that even though I subscribe to the del.icio.us/popular and digg RSS feeds, I rarely read any of the items, whereas I read almost everything from dive into mark or Jeremy Zawodny's blog. As far as the output is concerned, it doesn't have to be traditional "output" at all. It can be an increased PageRank for a site, or a Firefox extension that shows a reputation meter for every site you visit. The format isn't important, but the things people subscribe to are very important.