From what I understand, you have to drink a decent amount of it (it was more that 2 cups a day) to have the benefits. I don't understand the exact amount. Even without the weight loss benefit, it's supposed to have lots of antioxidants though, and it's better than coffee for you. I, however, will never be able to give up my coffee!
I have been drinking green tea for many many years, about 4 cups per day but not for weight loss, just because I prefer it. I can't see how it would have any effect on weight loss (you will note my "normal" starting weight), but if you were drinking tea in place of a beverage with calories, that would work!