"What really annoys me in books, media etc, is when someone states
that they stayed in "an" hotel for the night (for example) instead
of using 'a'."

Because that's a bit pedantic you mean? It is the older form, and still perfectly correct English, so long as 'hotel' is pronounced with a silent 'h'. "...the sort of thing about which we ought to be allowed to do as we please, so long as we are consistent" is how Modern Engish Usage puts