I had that rarest of things on a Cross Country Train yesterday - an announcement that passengers actually needed to hear!
I boarded the 1711 Leeds-Plymouth train, sat down and put my headphones on, but sensed something was wrong as, 5 minutes after our departure time, we hadn't moved and the screen on the patform showed our train as "delayed".
At this point the guard announced that, due to a fatality at Fitzwilliam, the train was heading back North to York and would then divert (presumably via Doncaster) to get to Sheffield. Knowing this would make me significantly late, I got off and headed for the 1738 Northern fast train to Sheffield instead.
And guess what? Hardly anybody on the train heard the announcement because they all had their headphones on! The guard even suggested that, if you had someone wearing headphones sat next to you, to give them a nudge and tell them what was happening. Which kind of proves the point made several times on this thread that, because there's so many pointless and unnecessary announcements on trains, when there's one you actually need to hear, no-one's listening!