I guess in the realm of PA's, less is more; More is obnoxious!
Anything that you wouldn't during an interview, you surely shouldn't say over the PA.
People pay for a safe, comfortable ride from point A to point B.
Some people want to be left alone (I fall in this category), some people feel claustrophobic and would like to occasionally know where they area, and others are heading out to vacation/coming home from and might want to know the weather.
So if it doesn't involve flight time, weather, route or delays or a mega high-profile playoff-style sports score, put the mic down!
BTW, when the girls sing songs on the SWA flights, it's annoying as heck!