Apparently there was some kind of storage glitch at Flickr:
We’ve had a temporary storage failure affecting a sizable chunk of old Flickr photos and are moving about 20 terabytes of photos across a few thousand miles (between two of our data centers) to ensure consistency and smoothness. ALL PHOTOS AND DATA ARE SAFE AND NOTHING HAS BEEN LOST. The site will come back up as soon as possible.
I’d post a screenshot of the funny “Arrggh! Our tubes are clogged!” image you get right now at Flickr.com, but, well, Flickr’s down. 😉
Best of luck to the Flickr crew in getting things back up and running soon. The blogosphere mob isn’t too kind when stuff like this happens (though people like me with an IT background are surely sympathetic).