I agree. I just bought mine off of eBay last night, got the code this morning, put it in Apple's site. I haven't gotten confirmation yet (I'll call in a day or so if it doesn't update), but with the live.com offer combined with BigCrumb (although I don't know if this went through), I will be paying $125 bucks for 3 year MBP!, it's a great deal! (if you are planning on this definitely look into the live.com offer, its an extra 25% off the already great deals). I think people who are warning against this bought it from apple and are mad because they didn't know they could save 100 - 200 dollars. I always research before paying MSRP for anything.
I bought Mac Pro AppleCare cover earlier this week from an ebay seller - got the code within a couple of hours, and got the email certificate from Apple within an hour. I've printed the certificate, along with the Apple Store invoice for my Mac Pro, and put them in a safe place.
Out of curiosity I too would be interested to know how someone can be making a profit on selling AppleCare for such a low price - I paid just over a quarter of the UK RRP. The old saying 'if it sounds too good to be true, it probably is' is echoing in the back of my mind!
I think the 'who cares' attitude is wrong. I care because I'd would like to know if there is any reason not to buy these codes from ebay - for example, if they're later found to be fraudulent and the Mac isn't covered; or perhaps if it turned out the sellers were stealing the boxes or codes from shops. With this in mind, receiving a sealed box certainly doesn't rule out the latter possibility.