Way too many people try to discredit BMI by bringing up the hypothetical trained weightlifter example.
It is possible to have a moderately low body fat percentage (12-15%) and fall into the overweight BMI category if you're very trained and muscular, but the number of people in this situation is very small. Moreover, they're well aware that BMI is not a useful indicator for them.
A 6 foot tall person would have to weigh 221 pounds to get all the way into the "obese" range of the BMI scale. A 6' tall man weighing 221 pounds with low body fat percentage is a seriously fit individual, not someone who casually goes to the gym several times a week. I don't think people realize how hard it is to get to this level of fitness.
BMI really isn't a bad for the average person, even if they lift weights.