This is a great utility. However as I've got my photos stored locally
and on the Flickr servers themselves, I don't feel too much of a need
to backup the photos themselves.
However: I've often wished I could backup all of the titles, tags and
descriptions I've written. Being able to store the comments and
notes others have written would be great as well.
I realize this might be beyond the scope of your app, but I think
there's a definite need for the ability to backup the textual information
associated with each photo as well as the photos themselves.