I only get about one match sometimes less. Tournagrip durability is not good. One reason for this might be the fact that you have to stretch it more then other grips to get it to cover the whole handle. I have changed to Yonex Super Grap it has a similar feel to tournagrip but is a little thicker resulting in better durability.
I'd say about a weeks worth. It depends on how much you play though. On average, a week sounds about right. I'm cheap though, I use to flip my Tourna over after one side got worn.
When buying tournagrip, I always purchase the Xlong version. It covers most handles easily and doesn't need to be stretched as thin. Cost is a couple cents more, but it is worth it.