In a pilot project announced Wednesday, the government archive put the public-domain, copyright-free photos on the Library of Congress Flickr page. That's just a small fraction of 14 million photos and other visual materials at the Library of Congress, according to the archive's blog, but hey, it's a pilot project.
If you're like me, you recognize the value of tagged photos when you're looking for a particular shot but can't remember when or where you took it, or when you want to sift photos to zero in only those with something like "birthday" and "grandma." But also if you're like me, you probably tag your photos only intermittently.
So it's a safe bet that the Library of Congress photos won't immediately sport a huge range of highly descriptive tags. But I'm inclined to see the glass as well over half full: having the photos easily available is great, and I can't imagine the government would pay on its own to fund some dedicated tagging effort.