A media company is using subpoenas to demand the names and addresses of anonymous Web users. That’s a story we’ve seen before. But this one has a twist or two. The media company is Grooveshark, an increasingly popular music service that’s also being sued by all of the major music labels. And Grooveshark doesn’t want information about alleged lawbreakers. Instead, it wants details about an anonymous user who posted comments on Digital Music News, an industry news site.