Yes, extended warranties DO have humongous profit margins - for the most part - but there are exceptions. I used to work at a retail chain that sells extended warranties on almost everything (and it was a big part of our job to sell them - though I also worked as a technician so I saw the value in them too) and our employee price on such warranties was 5% above cost. For instance, I got a 4 year iPod warranty for $6 that sold for $50 - a 4 year vacuum cleaner warranty for $3 that sold for $25, etc. Now I'll be honest - while I worked there, I bought the EP on almost everything - because you know, it was either really cheap OR the fact that it was near the actual selling price made me think it was worth it (plus I knew how to scam the system to get replacements and whatnot and use it as an upgrade policy more than a warranty). Certain items had expensive warranties even with the employee price, two of them to note: HDTV's (or any big screen/plasma/LCD) and laptops. The laptop warranty we sold was between $200 and $250, depending on price point (and that was before we get into the "platinum" options for laptop owners) whereas cost was in the $150 range. A $50 profit on a laptop warranty vs. a $100+ profit on a digital video camera (we sold it for $150 - employee price was $12 or something) tells you how often that warranty gets used, and it gets used a lot. The desktop computer warranties had a much higher profit margin (which makes sense - cheaper to fix and less problematic).
So - if you consider that regardless of manufacturer (Macs might be more reliable, but we're talking notebooks - and a Mac notebook now has essentially the same hardware as any mid to topline PC notebook - I'd like to think it is more reliable and better build quality, but who knows), even the insurance companies are only making $50 or so off of the plan (and that's what a warranty is - a third party agreement with an insurance company - same for Apple as anyone else - Apple just happens to do their own repair work, thus allowing them a higher percentage of the profit margin (even retail stores that have their own repair shops sometimes have to send off to a vendor)), it's probably worth buying.
When I bought my MacBook on Sunday, I bought Apple Care (I got $66 off thanks to my student discount - which was nice - and probably about whatever cost is on those things - or at least vendor cost, because third party Apple Care retailers online usually don't go too far below $184) - because if there is a problem in the next three years, the simple economics say that it will more than likely be a problem that costs me more than $200. If I were buying an iMac or a MacPro, I might not do it (Mac Pro - almost certainly not - I can fix anything that would go wrong myself and after a year, the parts would more than likley be cheap enough to replace without their warranty). LCD screens - for an Apple Display that are insanely expensive - yes - but a regular LCD or monitor - no way.
So is it worth it - well, for laptops - the profit margin is much lower than on other products - so I say it's a good investment.
However, I also like using stats, and they say that Applecare is a huge source of profit for Apple (and all others who sell them). Either way, we'll each do what we feel is right, because, it is OUR money. I can understand someone who won't have the money for a new logic board in 12 months saying that Applecare is good for them; it makes perfect sense. 
