Have quad-core processors arrived in the mainstream?

If you go out and purchase an average desktop PC today, you will end up with a dual-core system in most cases. But there have been quad-core computers on retail shelves for some time now and we have been seeing these PCs being offered for close to $800, which is generally considered the barrier between mainstream and so-called premium PCs. More such PCs are one the way – but what if you want to upgrade your dual-core system with a quad-core CPU? How expensive are these CPUs and are they actually getting cheaper? TG Daily took a closer look to find out.