Get the Most Out of Your Multicore Processor

Ooh, shiny! A new machine, and it has a Core 2 Quad processor! Everything's going to run so much faster now!
Or is it? When you have four processor cores, does that mean everything runs four times faster? Or is everything still running on the first CPU and ignoring the others? How do you find out, and how do you make the best use of that shiny new multi-core processor?
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