AmphetaDesk, an open source RSS feed reader for Windows written in Perl, was created by a programmer who was inspired by Radio Userland. As a result, it has a similar browser-based interface and saves some of its files in an early version of OPML.
After using AmphetaDesk for a while, I'm subscribed to around 45 feeds. Radio Userland can import these easily:
After you choose the file, Radio Userland subscribes you to each of the RSS feeds in the file. A dialog box displays the number of feeds that it found.