I know, I know. It's all that was available at the time this was announced, a little over a month before free accounts are scheduled to be shut down. Some people are probably already migrating.
Is it true that appfog's filesystem is volatile? Does this mean that it could be wiped without a system fault or a user shutting down the system? If so, there doesn't seem to be a clear migration path to appfog for PHP users that are using the writable directory support. If not, it should probably be documented that writes will only go to the one instance and that if you're using multiple app server instances you need to set something up.