We've seen in class that XML is an extremely powerful data sharing tool, but it should be noted, as with any information technology, that the benefits should still be carefully compared to the cost. Many people make the mistake of assuming that the newest technological breakthrough is always the best, whereas in actuality, that's highly dependent on the situation.
An excellent example of this is using XML for music. XML is certainly much better than scanning sheet music when collaborating with someone over the internet, particularly if the music then needs to be interpreted by a computer for a MIDI file or something similar. However, a local band simply sharing their sheet music with each other, not needing it to actually be interpreted by the computer at all, would likely be better served simply scanning the paper copy of the music than either taking the time to write it as XML, or buying a program designed to do so.
This is a rather silly example, but it does illustrate the point that any technology, no matter how wonderful, is never the solution for everyone. There are benefits, and there are costs, and it only makes sense to incur the costs if the benefits are ones that are useful in your situation.