Whats the bess live performance you seen? ;)
I remember the best one I saw was when I was in Toronto round this time last year. If you're familiar with the city it was in that big outdoor stage in the harbour where they have the market and the boats to the islands.
Anyway thery had some sort of world music festival on at the time, no Irish groups though, and there was this group from Pakistan called Rizwan-Muazzam Qawalli. They were a class act. All their songs were bout 10-12 minutes long but it was so energetic and intense for bout an hour an a half at half eleven at night. It was really unbelievable! :D