just to have a sense of security i would get it. If you are really tech savy and do well to take care of your personal belongings, then you can do without.
For my current (early 2008) MPB, I bought the $239 applecare. It has covered the replacement of three batteries, each valued at $129 by Apple. 3 x $129 = $387 - $239 = $148 net value.
They are if they're determined to be defective.Why did they replace the batteries? Batteries normally aren't covered with AppleCare.