yes there is a limit, sometimes, it can be pretty damn close to impossible to do so then others (depending on weed, method smoked, tollerance, among others)... you can actually smoke yourself sober, i've done it quite a few times... you don't actually just go 'sober' from smoking a whole lot in one sitting, it's usually over the course of the day, you can reach points where no matter how much you smoke, you won't 'feel' high (i only say it that way, cuz i'm not sure if you've just been dealing with being high all day and your used to it now, or if you really just can't get high) but then the next day, you can smoke even as little as a bowl and be stoned for hours again...