Many of the file formats I've designed have been in use for over a decade. Most have been through multiple revision levels and are backward- and forward-compatible (you can read an iMovie 4 project into iMovie 1, though it obviously won't understand and preserve all of what's in there).
The whole reason I've established this site is to call attention to the Emporer's New File Format and spark a conversation about information design. XML is not a good file format, yet it is widely used. Let's come up with something better.