I found this great thread on steam after initiating several experiments myself. For those tempted to inject steam into the baking process, one more forum member's experience is that it doesn't help much, if any. The opinions above are still true and good, IMO.
As you can see from the picture, I used a teapot and copper tube to shoot steam directly onto the pizza crust. You might remember that I use a rotisserie motor to turn the pizza stone, so the entire rim of the crust is exposed to a shot of steam on a revolving basis. I also use a hood over the stone to capture the heat from the burner below and the heat from the IR side-burner and cook nominally at 700F. (A post called rotisserie pizza grill shows the picture details.)
The test group consisted of four folks with an embarrassing amount of pie-eating experience. We cooked two identical pies, one with steam and the other with no steam, everything else was the same (throw temperature, cook time, etc). The consensus was that there was no significant difference. Only one panel member (me) thought there could be a tiny bit more crisp on the steamed crust – but I don’t trust that guy’s opinion as I know he has been wrong in the past.
So even though steam works well for bread baking, and even though steam has the potential to cook faster than a non-steam environment, and even though steam should puff the dough a little more, the difference in my tests is negligible. Don’t bother.