Personally, I never buy extended warranties.
In general, extended warranties are not worth it else the companies selling those warranties would be losing money. Electronics tend to fail early and within the standard warranty or last a long time. Mechanical devices (so the HDD and DVD drive) are much more likely to fail outside of warranty, but are cheap to replace.
That being said. Sometimes they are worth buying if you can't afford to be without the item and you don't have the cash to replace it. For example, if this laptop is for college use and you don't have the cash on hand to replace it in the next 4 years, then an extended warranty would give you the safeguard needed to make it through college even if you are just tossing the money away.