There an obvious difference between the PAs made while the a/c is on the ground and engines off and when the a/c is inflight. Often when I give PAs on the ground the flightdeck door is sometimes open and you can hear the PA very well, hence you know the PA system works well. However during flight in the cabin while positioning the flightdeck PA is often hit or miss.
As 'Rainboe' quite rightly said it all depends on where you sit, sometimes its easy to hear and other times its near impossible.
Whether its short haul/lowcost or long haul the story is the same which row/class you sit in makes all the difference. Listening to the PAs using the provided headsets on long haul flights is often the only way I hear the flightdeck PAs clearly throughout, mind you I only speak with economy class experience.
Granted the speed and accent of the pilot also makes a difference. The only comment I have had from a flight attendant regarding my PA was that a passenger told her that the crew must really be tired because the pilot said thanks for flying with 'X' airline when the name of my airline was 'Y'. I said to her no matter how tired I was there was no way in hell I would ever mix up my airline with Ryanair!!...
