I own a late-2006 MacBook. In its first year, the fan died and had to be replaced so I bought AppleCare when the one-year warranty was about to expire. Six months later, I had to send it in because it stopped booting. I have no idea what caused it, and Apple only has on file that they clean-installed the OS, but Im thinking it was a logic board replacement. My power adapter failed last year and I had to have it replaced under warranty, and then earlier this year my fans bearings started going bad or something and it was making a terrible clicking noise, and over the summer I had that replaced under warranty. A few weeks ago, I took my MacBook in to an Apple Store because the warranty was about to expire and there were a few dust spots in the LCD and the headphone jack was intermittently getting stuck in optical mode, and the Genius noticed it was much looser than normal. Apple replaced my logic board and LCD due to minor issues, as well as some other items related the the repair, all under warranty. Unfortunately, they reinstalled the bezel improperly and I have to send it in again, but repairs are covered by a 90-day warranty (or until the warranty on the computer expires).
If I didnt have AppleCare, my computer would not be in good condition. Im not sure if the logic board was replaced when my computer stopped booting, but if it was, that would have been a significant expense, and Im not sure if I ever would have gotten around to getting the fan fixed the second time if I had to pay for it, and I know my LCD and headphone jack would have issues for the life of the computer.
Its like health insurance. Sure, you may get lucky not having AppleCare, and save some money, but youll skip miss out on getting minor issues with expensive parts fixed under warranty, and if your computer turns out to be a lemon, youll be screwed.