Intel Core i3 vs. Core i5 vs. Core i7

The gang over at TechSpot have posted a comparison of the Intel Core i3, Core i5 and the Core i7 to give you an idea of what you get as you spend more on a CPU.
The Core i3 is intended as an entry-level option, the Core i5 is geared for mainstream usage, and the mighty Core i7 is meant for high-end systems and enthusiasts. Many will wonder which one is right for them. Do they need a Core i7 or will the Core i5 be just as fast for their needs? Should they spend less on a Core i3 and allocate the savings elsewhere, or is the Core i5 worth a premium?