This is hotly debated. Here is my approach to the question:
PowerBooks and iBooks (and other portables)
* Absolutely! Portable computers, no matter how careful you are, receive a lot of abuse. I am extremely careful with my PowerBooks, but they always end up going to Apple under APP at least twice.
Desktop machines
* Could be helpful. Most real issues will sort themselves out in the early days, but if you are likely to need to call Apple after the first 90 days, APP could be useful. If you buy an Apple Cinema Display, I recommend AppleCare, but you must purchase the display and the computer at the same time, as well as the AppleCare.
iMacs and other lower-end machines
* Again, could be helpful. Given the lower cost on APP for these machines, it really isn't a bad call, especially since iMacs have built-in LCDs.
PowerBooks and iBooks (and other portables)
* Absolutely! Portable computers, no matter how careful you are, receive a lot of abuse. I am extremely careful with my PowerBooks, but they always end up going to Apple under APP at least twice.
Desktop machines
* Could be helpful. Most real issues will sort themselves out in the early days, but if you are likely to need to call Apple after the first 90 days, APP could be useful. If you buy an Apple Cinema Display, I recommend AppleCare, but you must purchase the display and the computer at the same time, as well as the AppleCare.
iMacs and other lower-end machines
* Again, could be helpful. Given the lower cost on APP for these machines, it really isn't a bad call, especially since iMacs have built-in LCDs.