This blog post from the Library of Congress is indicative of the love and appreciation people have for LoC's picture stream in Flickr.  The first post is awesome too, especially this bit:

If you’re reading this, then chances are you already know about Web 2.0. Even if you don’t know the term itself, you’re one of millions worldwide who are actively creating, sharing or benefiting from user-generated content that characterizes Web 2.0 phenomena.

Oh heck, subscribe to LoC's blog and have fun browsing what your main library has to offer, picture-wise.  Great stuff!