I agree with all of the above. As usual, those are high level rules to avoid shooting yourself in the foot. The most important point is that there must be no loop introduced by the L2 device to which you're connecting your portfast port. In fact, I would not hesitate using portfast to a hub where only end stations are connected;-) (doing so to a switch would be much more controversial but potentially not impossible either).
Regards,
Francois
