I leave my tiles in the oven unless I specifically don't want them--
I'll remove them for delicate cakes, or sometimes if I am in a hurry
and don't want to wait the extra time for the oven to preheat.
I have what sounds like the same set, with thin bricks and an
aluminum sheet that holds them all. Nearly all of the bricks in my 2
sets are broken at least once, but they fit tightly together in the
tray and still work fine to bake breads etc. I often bake hearth
breads, and always do pizzas, foccacias and pitas, directly on the bricks.
--diane in los angeles
http://www.well.com/user/debunix/recipes/FoodPages.html