This thread has only touched on half of the story:

In the 1890's the leaders of the Irish political party Sinn Fein of Irish Republican Army fame decided that to speed up Ireland's separation from Britain that they needed to encourage the growth of a distinctly Irish culture. Unfortunately, like lowland Scotland, Irish cultural life was pretty much the same as English cultural life. Sinn Fein established the Gaelic Athletic Association and revived hurling, Irish football, and the Tailllteann Games. They sponsored Irish step-dancing, recitations in Gaelic, and musical competitions along with the Games. They decided on a national dress other than tweed caps or Kilkenny hats and grandad shirts, and wrongly looked to their fellow "Gaels" in the Scottish Highlands rather than the ancient leine and brat. Kilts, even now, are traditional for male Irish step-dancers. Since Irish pipers were really copying the Scottish/English military tradition, Irish pipers wore kilts when playing or competing. According to accounts I've read and photographs I've seen, Irish pipers in 1900s London competed on a regular basis and wore kilts of hodden, a solid color wool tweed, usually a medium grey. Nowadays, the pipers of the Royal Irish Regiment wear solid saffron kilts with a bottle green tunic and caubeen. The Army of the Irish Republic wear solid green kilts and caubeens. The often No. 1 pipe band in the world, Field Marshal Montgomery of Northern Ireland wear traditional tartan kilts with black Argylls and glengarries. NYPD's bagpipers are actually members of an Irish "union", the Emerald Society and wear solid navy kilts with gold piping. The FDNY pipers are also Emerald Society and wear tartan kilts.

Ironically, while the Irish and kilts don't go back a long way, the Irish and tartan do. The oldest known tartan in existance is the Clodagh tartan, a piece of which was used to stuff the neck of clay jar of rubbish found buried near Clodagh in Ireland. Various sources state that weaving tartan wool cloth was a major Irish industry with most, if not all of it destined and especially designed for the Scottish market. Only about 5 Irish families, all with Scottish roots, have their own tartans like Tara Murphy. Other Scots-Irish families can lay claim to clan tartans or Scottish district tartans. The Irish county and province tartans are not District Tartans in the strictest sence, but are more Trade Tartans meant to appeal to the buyer, though most are godawful ugly. Texas Bluebonnet is a district tartan because it was officially adopted by the State of Texas. Houston Bluebonnet was a mistake made by the mill but the Houston Fire Dept. Pipes & Drums bought it anyway. See also McLennium, Braveheart, Flower of Scotland, Scottish Heritage, ad infinitum.

On Irish-American culture vs. Irish culture:

I'm 1/2 Sicilian, 3/8ths Irish, and 1/8th Danish raised in central Oklahoma by a Chicago mom and a Texas dad, both Catholic, neither of whom really taught us anything about Italian or Irish culture, let alone Danish. We were just an American family, eating spaghetti and meatballs occasionally and putting up St. Patrick's Day decorations at parochial school. Once I became involved with the Highland Games, I decided to have a kilt made from material I had bought years before (a different story), but I bought as many Irish accessories as I could: plaid brooch, kilt pin, sgian dhub, waist plate, belts and buckles, and green flashes. Even though my Irish roots are still not very clear, I decided to buy a kilt in an Irish tartan and chose Munster Province because of it's beautiful colors, pattern, and symbolism and to cover my possible bases (Barry of Co. Cork, McMahon of W. Clare, and O'Hooley). If I could I'd buy a new Argyll and replace all the Scottish buttons with round Irish harp ones. I wear the kilt as a member of the Games and I wear an Irish kilt by preference. As a member of the local Irish American Heritage Association, I see the Highland Games as a substitute for the long-gone St Patrick's Day festivals and the Tailltean Games of ancient days. I've become so steeped in the lore of kilts and regalia, that I have to correct all kinds of misconceptions Scots have about Scottish history and traditions which is weird. I have also heard some of the cultural adjustments that people make when they emigrate from America to Ireland, my sister in particular who's now back in the US.

On people who take advantage of Plastic Paddies:

A shining example is Molly's Pub Downtown, formerly Slainte: Built in Ireland, formerly owned by Persians, and the most comfortable, best pub I've ever been in, with a friendly bartender from Ireland who closely resembled Michael Flatley. Another is the wily Ely O'Carroll of Clan Cian and his henchman, McCarthy Mhor, on the Standing Council of IRISH Chiefs who sold fake titles and a beautiful but not authentic tartan to the unwary American cousin.

For the Scots among us and kilt afficianados:

If you have a copy of Scotty Thompson's "So You're Going To Wear The Kilt", you absolutely have to have a copy of Jan-Andrew Hamilton's "The Emperor's New Kilt" just for the chapters on King George III's kilt and William Wallace's alter ego.

Slainte from the "token" Irishman on the Highland Games!