I'm a new TD owner myself, so I can't give you a 'veteran' answer, but I do know that we have a few hundred pounds of rear axle weight over a sedan, meaning that if a sedan only needs 160 pounds of sand to become a good handler on snow, then we should be fine with no additional weight. Especially if you have the third seat option (which is all behind the rear axle weight).
However, a bag of sand is helpful for pouring out onto the road to give you some grip if for some reason you get stuck, so I'll still be carrying one, just not worrying so much about weight distribution.
On my old VW beetle we used to put sandbags in the front.
The thing still weighed 1/3 what my TD does though.
peace,
sam