"What the VACUUM docs "should" do, it seems, is suggest CLUSTER on the PK, if the PK is a sequence (whether that be an actual sequence, or a timestamp or something else that grows monotonically)."
This is a case specific to you and this particular circumstance, not a general rule for VACUUM FULL. If for no other reason then it might make more sense for the application that the CLUSTER be done on some other index then the PK.
On Stack Exchange, I've got a question on how to determine when to run CLUSTER. It ties in strongly with this thread..
