Does it really make more than creating ads and targeting them appropriately at the right interest groups (i.e. advertising footballs on a sport fan site)? Asid

Does it really make more than creating ads and targeting them appropriately at the right interest groups (i.e. advertising footballs on a sport fan site)? Aside requiring snooping to be effective in the first place. Are there good studies on this to validate it? Companies spend a mint on this stuff because they are told it works and is necessary, I'm not sure that's true, especially when that comes from the sales/marketing arm of those ad companies...