Priority boarding is very inconsistent, AF did not pre-board my last BOS-CDG flight, NW often does not pre-board if there are too many Elites on board etc. I found CO to be pretty good with this perk, never seen them not to do Elite pre-boarding. It can get to a problem if there are too many Elites on a given flight, I have seen a number of airlines limiting it to Gold/Plat or Plat only.