I agree with Schweb but I'll also add that if you have any screens (monitors) you might also want it for the sole purpose that the monitor will cost anywhere from $500-$1000 to fix out-of-pocket whereas the Applecare warranty will fix it for free.
In this day and age of technology, nothing is guaranteed to work for a specified length of time, regardless of the company making the product. For a couple hundred dollars now, you can insure that you won't have to pay to get your item fixed if something (within the warranty) were to go wrong.
Just my 2 cents, and no I don't get paid for this advertising, I'm just a happy customer.