In America, f*** is universally considered to be one of the most offensive curse words known to man.  That’s not to say that it isn’t said on a regular basis by many Americans, but for many it is considered taboo.  In Ireland, the “F” word is far less demonized and used much more casually.  I wouldn’t put it on a par with everyday slang, but it’s pretty close.
I hear the F-bomb daily in Ireland, and find myself peppering the occasional sentence with it as well.  I hear it when eavesdropping on conversations in the library, on primetime television, and in casual conversations with colleagues at work.  For most Irish people it is simply a colorful adjective, as in:  “For f***’s sake”, “That’s f***ing brilliant” or “the poor f***er.”  I have rarely heard it used in an aggressive manner (e.g. “F*** you”).  Well, there was that one time when we saw a fist fight on Barrack Street between two cab drivers.  F*** was definitely not being used in an affectionate or casual manner that time.
Pat and I remember clearly our first bit of craic in an Irish pub.  We were in Passage West, a small town outside of Cork.  It was lashing rain, and we were at the mercy of the bus which wasn’t due to arrive for another couple of hours.  Since walking around was out of the question we popped into a pub for a drink and some warmth.  We were the only customers in the pub and the owner, Simon, seemed glad of the company.  He sat down with us by the fire and began to chat.  He was incredibly friendly and welcoming, but about every third or fourth word out of his mouth was f***.  To him, it was just another word – a word that he liked to use a lot.
I find it rather amusing and appropriate that an Irishman got away with using the F-word on prime-time American television.  During the 2003 Golden Globe Awards, Bono of U2 fame, said, “This is really, really, f***ing brilliant” on the air while accepting an award.  Somehow it didn’t get bleeped out, and the FCC decided not to make an issue out of it.  Apparently, since Bono used the word f***ing as “an adjective or expletive to emphasize an exclamation”, and not to “describe . . .  sexual . . .  activities” it was okay.
Many Irish use the word feck, as well.  If you google the word, you will see that it has a variety of definitions that are not considered expletives or slang, but in the context of present day Ireland it is used exclusively (in my opinion) as a substitution for f***.  Follow this YouTube link for a Father Ted clip and see what you think.