Is the Facebook app's option "Connect with my phone" currently enabled? I had this problem when I first installed 8.1 preview, and even though it pulled down the 8.1 Facebook app, I had to uninstall then reinstall it before it would let me enable the "Connect with my phone" option, at which point it synced, and my contacts' pictures showed up again.
(this assumes you're working from a system where you're merging your Facebook contacts with your phone contacts, and all of the pictures are pulled from the Facebook profile image)