With motherboards like Nvidia 680i and Core2Duo processors overclocking has reached a new dimension. Now even the manufatures support overclocking. Many custom PC builders sell their PCs pre-overclocked. This was not possible earlier. Also you dont loose your waranty now if you overclock. Its lot safer now.
One of my friends overclocked his E6600 to 3.4Ghz i.e. by a full gigahertz although for such overclocking you need liquid clocking.