I get pretty great battery life and I'm a heavy user. On average I get about a day/day in a half without charging and I think if I had a bad battery I wouldn't be getting that kind of life out of it. I also don't believe that I have 266 charge cycles, just doesn't seem possible to me.
I don't know, if you got it a couple of weeks after launch and you get a day/day and a half out of it on average, then doesn't the math work out pretty accurately at 266 cycles?