March or April with the introduction of the Core i7 980X, but as the processor is $999, and the cost of DDR3 is inflated at the moment, you won't see them in many boutique PCs, much less the ones people build for themselves.
AMD is also introducing a hexa core processor around the same time, presumably name the Phenom II X6, but it's currently known by its codename, Thuban. Also, as the IMC on Phenom II struggles with larger memory capacities, it's likely that Thuban-based PCs will top out at around 8GB.
Outside of 2010, I doubt we'll ever get all that many hexa core CPUs. Octal core chips will be the name of the game in 2011 with the launch of Bulldozer and Sandy Bridge, while those chips which come off the line with bunk silicon will undoubtedly be knocked down to quad core.
If anyone is going to make a hexa core chip next year, it's probably AMD. They need every penny they can get far more than Intel does.