Don’t know why this isn’t more widely published since Jeremy blogged it last month. Yahoo! exposes the OPML which allows you to export your RSS feeds (if somewhat crudely) from Yahoo!
The OPML page is at http://api2.my.yahoo.com/2.0/content/getsubs (you have to be logged into Yahoo to use it)
At the moment, I’m only using the export feature to put together my blogroll. While there are plenty of things I dislike about the Yahoo! RSS reader (it poorly tracks which entries you’ve read, it requires multiple clicks to add a new feed by URL, it lacks tools to manage, tag or categorize, it’s hard to tell when entries were posted), I do have faith in Yahoo’s ability to iterate improvements, so I’ll stick with it for now.