I've never purchased Apple Care (original iMac, Titanium PowerBook, Dual G5, iPod 4th gen, various Macs at work). While I've been lucky, we've had some problems with the Macs at work, various weird problems.
The way I look at it, hardware problems will most likely happen with moving parts, like the hard drive and optical drive, and those are cheap. I recently replaced a hard drive on an out-of-warranty MacBook Pro for like $80 (self-installed). Over and done in a day. If I had to bring it somewhere or send it somewhere it would have taken a lot longer.
Still, I just bought a black MacBook off eBay. Seems in 100% good condition, but I might get AppleCare if I can buy it cheap off eBay.