Those instructions are great for pizza, but not real practical for
other things. If you leave a pizza stone in the oven all the time, it
will take your oven *forever* to heat up for regular cooking. It does
tend to regulate the oven temperature so if your oven's a little flaky
(gets too hot then too cold then too hot, etc while baking), then by
all means leave it in, but let it warm up for a good half hour before
popping the food in.

I use my pizza stone on the rack at the lowest level of the oven, with
the oven as high as it will go (I think mine's 500). I start it
pre-heating around the time that I punch down my pizza dough, if not
before (I frequently let the dough rise in the oven with the heat off,
since it's not so drafty, so when I take it out, I turn on the heat).
The dough then rests for at least 10 minutes before shaping and
topping. Generally I end up with a minimum of 20 minutes of pre-heat
time on the stone. I use parchment under the pizza, not to save the
stone but for the pizza peel. I do fine getting one pizza in and out
without parchment, but the second pizza always sticks to the peel and
ends up upside down on the stone. My pizzas tend to take around 10
minutes to cook, depending on how thin I stretched the crust (I don't
do the real thin crusts).

For frozen pizzas and re-heating, don't bother with the stone. Just
use a perforated pizza pan or regular cookie sheet.