When you shop throughout Ireland, many places offer duty-free purchases. In these cases, they'll either remove the tax at the time of purchase, or you'll have to submit to have the money returned to you when you leave Ireland. In that case, you'll receive a tax form -KEEP TRACK OF THEM. You'll need them to receive your refund. You can either turn these forms in at the airport and receive a check or a refund on your credit card, or you can mail them back, which takes about 6 weeks. I don't know about you, but I chose the airport/instant option.
Make sure to plan time for that when heading to the airport. It took us about 20 minutes just to find the duty-free window, then we stood in the wrong line for 10, then we stood in the right line for about 10. You have to fill out lots of forms and such, so have a pen handy.
I had about $70 of purchases and received about $5 back on my credit card. Not the biggest refund in the world, but $5 is $5.