Recently, d.facdn.net (ie. images and other artfiles, as well as thumbnails), began being served over HTTPS, for no obvious good reason. Despite the intermediate SSL certs being broken (which leads to certificate errors on certain types of popular smartphones), this adds additional load to an already overloaded infrastructure. d.facdn.net resolves to a single box in the netblock owned by Ferrox Art, LLC. This is not new, but it also means that the additional load of HTTPS is being borne by that same box, and not, say, by some kind of cloud-based caching service.
At least one Twitter user this morning said they'd been prompted to enter a reCAPTCHA challenge with the message (ostensibly from FA) that their computer had a "virus".
And now, the administrator notice, in addition to informing users about AUP changes, is also stating that the administration is aware of performance issues and that their may be "unplanned" maintenance this week to fix it. Which is progress, I guess, that they are more or less willing to admit to winging it when it comes to this stuff. Translation of "unplanned maintenance", to me, is something like "Whenever Dax feels like it/Whenever Yak is awake".
Maybe you could solve your performance issues by not using SSL when it adds no value whatsoever, and you don't have the fancy hardware and software necessary to lighten the crypto overhead? What exactly is being protected by the SSL session? There are no cookies sent to the artfile server, there is no login whatsoever necessary if you know the direct link to a mature image. All of this is as it was before. Except for the SSL.
It might make (slightly more) sense to make the main domain end-to-end HTTPS, to protect against cookie hijacking. But SSL-izing facdn.net is the one thing that makes no sense to me, and it seems to me to be the one thing that could be (maybe the only) cause of their current performance issues.