lfcjfc,
I have just flown from and returned to Shannon over the week-end and had no problems with parking. Hint - as you drive into the airport you will have the long term carpark on your right, you can slow down (don't stop or obstruct other users) to have a peep around the carpark for spaces before you enter as sometimes the airport authorities put up signs urging users to use the 2nd longterm carpark - anyway, this is just a slightly longer walk.
BTW, I was talking to some of my fellow travellers on the return trip and they said that there was delays on the security desk at departures on Friday morning - maybe there was extra flights.