Seems to me that it is likely that the net weight will go up substantially with the liquids ban. If a person is ready to either get liquids/gels at the destination, or replace her liquids/gels with other products (e.g. powdered toothpaste), then the net weight for that passenger is a wash or close to a wash.

However, if she is not ready to buy at destination or eliminate all her liquids/gels, then she's resigned to checking luggage. And once the decision is reached to check luggage, then the floodgates open to say: screw it, I'll pack in my large suitcase instead and bring those extra clothes, extra shoes, and extra books.

At least that's the logic tree I'm going down for my flights later this week.