I have to declare an interest here in that I am half Irish, was actually born in the place and still have many living relatives there as well as here in Scotland and the rest of the UK.
I note that a few contributers tell us they have "Irish blood" and that is, no doubt, the reason they feel a strong affinity to the country and its people and traditions. They should not, however, let this blind themselves to the true facts of the situation, namely that kilt-wearing is not, and never has been a facet of Irish custom. It is true, as MOR has so eloquently stated, that people from the north-east of Ireland (along with Viking settlers I might add) settled the western seaboard of Scotland from Galloway northwards, extending the kingdom of Dal Riata. The two communities on either side of the North Channel between Ireland and Scotland maintain strong family connections right up to the present day (I am just one of many examples) and in past times it was common for Scots gallowglasses to fight as mercenaries in Ireland. Despite these close connections, however, and the sight of kilted Scots over for a battle or two, kilt-wearing was never adopted by the native Irish and, to this day, the only kilts you will see there are in pipe bands, some Irish soldiers and (only very recently indeed) at the occasional wedding. I have never seen a kilt worn outwith such occasions and anyone wearing one would immediately be assumed by the locals as being Scottish.
It is best to learn the true facts and, preferably, have some personal experience of the situation on the ground before jumping to a conclusion which suits ones heart rather than ones head. This should not, however, debar anyone from wearing a kilt wherever they feel their true identity lies but they should not try to manipulate history to suit their own aspirations.