I recently decided that I would like to have some kind of tool that I could run to backup all of my photos on Flickr. I basically wanted a directory containing a bunch of subfolders representing sets, with the original photos placed within. I also wanted all of the photos that I had not placed into a set to be downloaded.
Solution: flickrj.
Over the course of the weekend, I’ve become a developer on the flickrj “team”. You gotta love open source 
“Hey, maintainer. Are you going to fix bug x?” “No, user, I’m busy. Do you want to do it?”.
So…if you are a Java coder, and want to do neat stuff with Flickr, do check out FlickrJ. My backup program is also up there, checked into flickrj’s CVS repository.
Update: The actual backup application is here: http://cvs.sourceforge.net/viewcvs.py/flickrj/api/src/flickrj/samples/