We were there two years ago. It was a tremendous trip. In no particular order (well, actually the order in which they're coming to mind), our highlights included:
The Irish Craft Beer Festival - not all that big, but then not massively overcrowded. One fun thing was meeting the Irish homebrewers. My wife is on the AHA Governing Committee, and at the time I was the president of our local club. Somehow the two of us talking to them got twisted into a message to their other members that "the President of the AHA is here!" It was a hilarious misunderstanding, and one guy asked for my autograph thinking I was Charlie Papazian.
My favorite beer was Metalman's Irish Pale Ale. We got to meet their brewmaster. I don't remember her name, but my wife was stoked that it was a woman.
We loved Galway. Galway Brewery has a beer named Hooker, named after the local fishing boat that has an upturned prow that looks like a fishing hook. My wife spent a lot of time trying to buy one of their T shirts that said "Call for a Hooker".
We took a ferry out to the Aran Islands. They were very, very cool!
Visit a fairy ring, preferably with a local guide who can give you some history.
The tour at Guinness is middling. The visit to the bar is great. The tour at Jameson's was a waste. The tour at Smithwick's was great, but that location is now closed.
Non-beer: Cliffs of Moher, Rock of Cashel (sp?), and the bus tour of Dublin were all great.
You will have a great time! The Irish people were very receptive to Americans, and it was the easiest European country we have visited in terms of understanding how to do stuff and get around. Apart from being on the wrong side of the road. Roundabouts in the wrong direction are scary!