TreeHugger pushes higher density living, but one thing people complain about is noise. It is hard to build a really soundproof wood frame partition wall, but new products like Enermax can make a big difference. It is a 1/2 thick fibreboard sheathing with a foil face. Bonus points: CFC and VOC free, it's made from 98% waste fibre with a corn based binder.
Not only does it cut sound significantly, it insulates too. It isn't hard to use or expensive to purchase: "Enermax provides maximum soundproofing at minimal cost because it's a simple product manufactured from recycled materials."- wood fibre with a foil face for extra reflectivity.
The effectiveness of a wall is measured by its Sound Transmission Class, or STC rating. it is based in the reduction in decibels through a wall; if an 80dB sound on one side is measured as a 30 dB on the other, then the wall has an STC of 30. Since the dB scale is logarithmic and a 10dB reduction is equivalent to being half as loud, going from a standard residential wall of STC 50 isn't going to do much if there is a home theatre on the other side. However if you spend a little money for the double studs and the enermax and you can have a quiet room no matter what the kids are doing on the other side. ::Enermax