How much of a detriment do we think the departure tax has?
I have a few pals at work (here in London) from Westport and they will often fly to Knock, but come home from SNN or DUB as they say "You have to pay extra to fly from Knock".
Last year I flew to Knock but flew home from Dublin. Admittedly that was to try the new Southend service :-) but I do remember the feeling when I read about the extra charge. It wasn't to check what the overall taxes were.