My only major delay on an Aer Lingus flight was a flight home from Amsterdam one Christmas several years ago when Schiphol was snowbound; my Cork flight was cancelled while I was waiting in the lounge, but they put me on a much-delayed Dublin flight which had been supposed to leave hours before I even got to the airport, and which finally touched down in Dublin after 3am the next morning.
I guess every airline has to contend with the occasional technical delay. How did EI do?
My first ever KLM flight was a Cityhopper flight to Vienna from Amsterdam, many years ago; we were bussed out to the Fokker farm and boarded, only to be bussed back to the terminal some time later, after the captain realised we wouldn't be going anywhere on that particular plane. Despite this being KL's home-base no replacement aircraft was forthcoming; I was rebooked to travel the next day, with no mention of compensation or EC261/2004 (which, at the time, I did not know about).