I would certainly not get out of my j/s if cockpit had announced "prepare for takeoff". For MY safety.
In the upper deck out of Frankfurt a couple of weeks ago, I was in 15B, doing a crossword and listening to channel 9. One of the F/A's was gregariously puttering about the cabin after doing the safety demo, picking up cups, arranging things, making people comfortable. I didn't pay much attention, since I was after all doing a puzzle.
We were a few minutes late off the gate, as I recall, so the taxi was brisk but not uncomfortable. As we were making a turn on one of the taxiways, I remember thinking "say, didn't I hear us get a takeoff clearance and a climb restriction a minute or two ago?" I looked around, saw that we were quite near some tarmac with white paint, and thought to myself "MrLincoln, that's one
BOLD flight attendant over there."
Fortunately he was near the jumpseat about three seconds later, when the nose gear straightened out and all four of those engines went to takeoff power. The look on his face as he spun into his seat on one heel -- facing a rather surprised couple in 15G/H -- was worth the price of the V fare.