I have been known to encourage the booking of flights mostly because I want to visit the Mac shop, as opposed to actually wanting to go on holidays. It's great - they seem to have made it a bit smaller recently which is a shame - but I can get over that considering the amount you can save. Which then of course means you can buy more! No trip is complete without me bagging at least a couple of eyeshadows or a gloss or three. They also seem to have a pretty good compliment of all those other beauty essentials that Mac do so well - foundations, brushes, powers and applicators of all descriptions, but I usually go straight for the bright colours.
If you can't wait for your next trip abroad then there are 2 other Mac concessions in the Dublin area that I know of as well - in Brown Thomas on Grafton St. and in BT2 in Dundrum town centre.