Version:           0.9-svn 2006-09-30 (using KDE KDE 3.5.4)

It seems sorting the images by the EXIF date tag doesn't work for image files - either because digikam can just sort by file creation/modification date (which is what it also shows below the image file) - or because it doesn't read the exif date tag in Nikon D70 .jpg and .nef files correctly
 
I hope this gets solved as fast as possible ... 
 
I use Nikon Capture in wine to do the raw processing, and Nikon Capture saves it files with the real file modification and creation date - but keeps the exif (just adds what was done when raw processing) - so by professional software it is meant to be done like that: 
Use file dates when they were really saved/processed/modified, and use the exif just for what it is meant to be used: to see when the image was taken 
 
So you should be able to sort by: 
- Picture taken (exif date) 
- Picture modified (file modification date) 
- Picture created(if it was processed from raw it is different to the "Picture taken") (file creation date)