There's been some buzz about the Library of Congress putting images on Flickr, and the Life/Google partnership, but now the German Archives is putting 100,000 images up on Wikimedia.
It's an interesting choice. Flickr is popular, but so was AOL and Compuserve once. Google is the big dog, but keeps things in their silos (Google Books). Wikimedia has the advantage of international support and a foundation, so it may be a wise choice. It's certainly cheaper than having your own server farm, and provides redundancy. And I'm sure some of those images will end up on Flickr and other sites, for more redundancy.
I've always been a belt-and-suspenders person, so this looks like a win-win situation.