Ireland is completely different to the UK in this area.
If the shot you take is of a OPW property and you are on public ground, there is never an issue.
The OPW are fairly under funded and they do like to avail of a bit of extra income from photography, and if you are profiting from the shot on their property then thats reasonable I think.
I did a fashion shoot in front of an OPW country house one time and the officials came out to see what the fuss was [model, makeup artist, hair, etc all around]
They asked if it was a commercial shoot and if I'd permission. I said that I didnt have permission and that I wasnt contracted for the photos, that they might be published later though. I said in that case I would contact them and pay them whatever fee was due and also gave them my contact info. They then asked me if i needed any help to just ask and were very polite.
I've read horror stories from a few places around the world but thankfully Ireland has not come down to this level.
I remember a few years ago taking traffic trails at dusk of a motorway sliproad. I standing in a roundabout and was thinking I might get into trouble for this when the next thing I hear a siren and then see a blue flashing light heading my way and a big police 4x4 pulls over and the cops ask what i'm doing. I tell him about the traffic trails and he then says "fair enough", "is that a hasselblad?" I said yes and he then says it looks just like a radar trap, starts laughing manically and drives off and waves.
Prisions, courts, schools, playgrounds and inside shopping centres are the only places I think you would be hassled.
Historic sites depend on tourism and what tourist doesnt bring a camera?