This is a utility I created to organize photos from my digital cameras
into directories based on the date the picture was taken (as per the EXIF data).
The metadata library is JpegMetadataReader, which apparently is now known as
metadata-extractor (http://code.google.com/p/metadata-extractor/).  It uses
log4j for informational messages.

To run it, just feed it the source directory and the target directory.  It will
recursively scan <source> for *.jpg/JPG/JPEG/jpeg files and move them to a 
subdirectory of <target>.  If the photo was taken on Jan 4th, 2009 and the file
is named IMG_0023.JPG, it will move the file to: 

	<target>/2009/2009-01/2009-01-04/2009-01-04.IMG_0023.JPG

This makes it easy to find photos taken on a specific date, whether or not you 
use software like Picasa or iPhoto, and prevents having thousands of files in a
single directory, which can be a huge pain.

There's also a utility called AviOrganizer, which does essentially the same, 
but for *.avi/*.mov, and rather than using EXIF data (which they don't have)
it uses the file's modification time.