Make sure that your warranty covers manufacturing defects and other problems. Find out where you'll have to take your computer for repair. If it has to be shipped back to the manufacturer, you may be in for longer delays. Check the technical support policy of the manufacturer. The better deals will give you a year's worth of phone or online help.
Service contracts extend the warranty, usually by two years.
Ask if the major components of the computer are covered. Some service contracts cover only the less expensive elements, and not the operating system itself. Most people buy service contracts because they provide peace of mind, in addition to the fact that they may have felt pressure from the salesperson. Consider the fact that salespeople at large national chain stores are often paid a bonus when they sell an extended warranty package. This Web site covers a variety of consumer topics, including tips on buying a computer.