I think it's really interesting phenomenon. My father definitely has quite a few stories from his childhood about being harassed for being Irish in the 50s/60s.
I myself was under the impression that it was pretty much gone with some lingering anti-Catholic sentiment, but there was an interesting discussion on jf about some areas with more active anti-Irish prejudice.
I think part of the reason why the St. Pat's stuff doesn't bother people as much because it's basically been embraced. There's definitely been a certain fetishization of having a Celtic background, even if it's only an 8th or less.