One common use-case for multicore processing on the desktop and elsewhere is “doing many things at the same time”. You could be running many user-interface programs at once, like the “typical today’s teenager template” of tens of IM clients, web sessions, email conversations, music and video players, downloading movies, etc. Or it is a more business-like background indexing of harddrives, backups being taken, downloading large business files, compiling software, updating source code repositories, etc.
I have been doing both of these modes to some extent, and the main problem with them at least on a PC is that while the processors might be good at multitasking and sharing the CPU load, my IO system is annoyingly non-parallel.
A company called Fastscale Technologies has a product that is simple in concept and yet very powerful. Instead of using complete installs of heavy operating systems like Linux or Windows to run applications on virtual machines, they offer tools that provide minimal operating system configurations that are tailored to the needs of a particular application. Since only that application is going to be run on the virtual machine, this is sufficient. According to press reports, this means that you can run several times more virtual machines on a given host, compared to default OS installs. And boot an order of a magnitude faster.