Why Dual Core Processors?
Processors with two cores are the future, because parallelizing computation increases performance much more than any incremental clock speed gain ever could. While 4 GHz is doable from a technical point of view, the disadvantages such as huge thermal dissipation, large cooling requirements and high energy consumption speak clearly against it. Eventually, CPUs will go to four cores and even larger numbers.
The key to increasing performance lies in the thread-optimization of applications: Modular software based on multiple threads can be executed quickly by distributing these threads to all available processing units, a process called multi-threading. Operating systems have been doing this on an application level for a while, by assigning processor time to different applications, which is called multi-tasking. With two cores, your computer will be much more responsive and is unlikely to stall at any time due to a single task consuming a lot of processor resources.
It is logical to assume that two processor cores could also draw twice the amount of power, but that is not the case. Although they do require more power when both cores are under a high load, the dual core will finish multi-threaded tasks much quicker than a comparable single core processor. This will result in a total power consumption that is usually below the total power draw of a single core CPU. In addition, the CPU makers need to meet their platform specifications and can only change these when a new platform revision is due. Also, more processors use energy saving mechanisms that will put unused processor units to sleep while they are not in use.