AppleCare doesn't make it last longer. It's just an expensive insurance policy with often high deductibles. If you manage a fleet of Macs it's much cheaper to just keep extras on-hand since most AppleCare claims require two shipments to get it fixed and you need something to use during that time.
Personal usage it is still an issue. If you have a problem you to send it back in most cases and be without a replacement. The best move is usually to buy a new one, time machine over to it, use it during the repair window, time machine back to your original after the repair and then return the new one. Still unless you are a total basket case with the care of your laptop you are better off saving your money.
