I don't think our Thanksgiving is a carry over from Ireland. I could be wrong though.
I NEVER shop the day after Thanksgiving. My wife used to be the head customer service manager at the busiest WalMart in the world. She wasn't fit to be shot when she got home the night after Thanksgiving. She has a government job now, and we can actually enjoy Thanksgiving because we can go see family and not have to be home in time for her to be at work at 2AM the day after.
I generally shop close to Christmas, unless I'm going to try to get something hard to find for someone. We always go out on Christmas Eve to shop, because back when we were really broke we couldn't afford to do Christmas shopping until I got my generous (seriously, it was a generous bonus) Christmas bonus at the shop party on Christmas Eve. It became a tradition we share together.