There are some advantage from multi-core processors , with time application became multithreaded and benefit from both core, as daily use application i note for example winrar , 7zip , photo-shop etc... witch show nice boost using dual core or multicore processor,
For the moment most multi threaded application are optimized for dual core , there is not much performance boost from quad core for example in home application, (But in server this is another story).
Game recently started to show improvement with dual core processor, for example quake 4 , and the soon released unreal tournament 2007 witch will bring the new 3d engine level
Hope this help.
In a word two is better than one , four is better than two and so on