Warranties are generally grossly overpriced, and a high profit item for retailers working with a very close mark up. But the worst part is the sub-par service that they may offer. Frequently, unless the repair is made by the manufacturer or is a complete replacement of the item with a brand new one (not "refurbished"), the problem may actually remain or worsen in a not so obvious form, or a new problem (or problems) may have been created in the course of the work. Generally, repair personnel is simply not up to the complexity of the product, and unless the components are modular, the service company may not have the ability to match the configuration and quality of the original work, especially when the product's components are tightly installed in very close quarters.
Lastly, and perhaps more importantly, is the steady advance of new technology coupled with decreasing prices for same. By the time your DVD drive is repaired and hopefully operating properly, you can purchase an external higher speed double layer one with all the required software for considerably less than your original. While we abhor built in obsolescence and "disposability", who's storing files or data on floppies today or even using 100mb zip drives in the face of CD-R/RW?
For the above reasons, I generally avoid purchasing repair or service contracts, except for very expensive items with highly sophisticated technology, and then, I carefully choose only an established and competent provider which is hopefully supplied or authorized by the manufacturer.