Moving from the US people often ask me my opinion on the cultural differences between Ireland and the US. It's hard to compare the countries as a whole, due to the cultural differences within each region of each country. Just like there are cultural differences between Northern Ireland and Southern Ireland, there are strong cultural differences between the northern US and the southern part of the country. It is a little easier, however, to compare the differences between Seattle and Dublin.
There are certain slag words like people saying, "what's the crack?" when asking how is it going. Or really using the work "crack" in general as slang for something good versus a highly addictive narcotic.
The mass transit system is more efficient, which is annoying because the US is considered a first world economy, yet we rely on interstates jammed packed with SUVs for transportation. In Seattle a pedestrian will walk out into the street daring the car to hit them, knowing the driver will stop. In Dublin not only would the driver of the car hit the person, they would get out and yell at the person for being a dumb-ass and walking out in front of a car.
For the most part, however, it's the little differences. There are no extra large grocery stores where you can buy furnishings along with your food. And for a country that has such a long rooted history with religion they are very liberally minded on most subjects. Except for the quantity of alcohol in a mixed drink, which is always a measured shot. Never a poor by hand.
The city is heavily populated by every country around the world so that you can be out with a group and potentially not have two or more that are originally from the same country. One of the things I wanted to do when moving here is pick up an Irish accent, but I have found this hard to accomplish as I don't hear enough of an accent from others to be consistent about it.
And of course when you order fries (chips) they almost always offer a choice of ketchup or mayonnaise to dip them in. So that no matter where you are from, you can dip your potato product in the sauce of your choice.