FWIW, yesterday I saw a "fail whale" page on Flickr for the first time ever (though it was of a baby panda). I don't know if that's a consequence of infrastructure changes or increased traffic...I don't think it's the latter but perhaps the increase number of fetches on each normal page load is causing a burden.

Also, the simple prev/nav between single photos has always been unacceptably slow...hopefully that gets fixed, as that's also kind of key to the viewing experience