I was intrigued by the Mario Batali PIASTRA granite cooking stone sold on Sur La Table and all over the web. The idea is that you use it on your grill and it conducts heat like cast iron etc etc... I personally leave a pizza stone in my oven pretty much regularly as i like that versatility - this sounds like a similar concept, yet for the grill. I wonder if i could just get a scrap granite piece from a local marble/tile vendor for a fraction of the cost?? Yes the batali piastra has the one flat side and one griddled side which is interesting - but any thoughts on this? Does anyone own a Piastra??