You can have them down until the plane shuts the door and pushes back. Since 1st class boards first, it's not unusual for people to have their trays down.
Actually, on Continental 737's and 757's, the trays in First Class don't come down, but rather they are stored in the armrests. They fold up and out and are hinged in the center so you can have only half the tray out or all of it.
It is the general custom for the flight attendants to place pre-takeoff drinks on the front flat area of the armrest between the seats (there is a small pull out tray at the front so that two drinks can fit). As you said, having your tray out during taxi is not allowed, but I rarely see people take out their trays before the door closes and I fly an average of twice a week on Continental so I do sit up front around half the time.
Actually, if Mrs. Osteen was calm and cool, I would think that someone who had been upgraded would have volunteered to give up their first class seat for the sake of getting there on time instead of having to sit and wait for their bags to be offloaded. I know I would have.
Exactly. I always see people in first class, with trays down to support the free drinks they get. They usually give me a disdainful glance as I trudge back towards my seat in steerage, as if they are afraid I might leave a bad odor behind me, which will interfere with their enjoyment of their beverage.