Is it OK to move a light aircraft by pushing or pulling the propeller?
A couple of my CFIs have asked me to help them park the airplane (in absence of a tow bar) when I was pushing the airplane by putting one hand on the hub and the other on the propeller near the hub, and them (the CFIs) pushing the tail down and nose wheel elevated. But according to AOPA, it is not a good thing:


  ... never push or pull on the prop blades. Forget what anyone has told
  you about pulling near the hub or the strength of the propeller.
  Aluminum blades can bend, and it doesn’t take much to put the blades
  out of track with one another.


This PDF says the same thing:


  Avoid pulling the airplane around by the prop. Yes, this seems the
  perfect solution to a vexing problem of how to change the airplane’s
  position without having to walk around and get the tow bar, but it’s
  worthwhile to make the extra effort. Neither the engine nor the prop
  particularly benefit from the loads imposed by horsing the whole
  airplane around.