Thanks for the feedback.  That would be pretty cool, but I don't think that data is available anywhere.  I can get notifications through the Spotlight back-end of when files are modified, but I don't think I can tell which application modified them and how much data was written.  There is a command line tool to show all disk I/O by process, but it requires root permissions, which I want to avoid requiring in my products (both for security reasons and so I'm not requiring additional information from users).

If I do find a way to do this without root permission, I'll consider adding it in the future.