Have you double checked that American Express will actually give you that extra year? Credit Cards usually extend the base warranty of the system (if it is not refurbished) but will generally not extend any extended warranty you have purchased.
Yep. I had this discussion re: AmEx warranty extension on MacRumors before, and I double-checked with a two separate reps. The year extension I get on top of the AppleCare 3 years is the basic Apple (manufacturers) warranty type coverage, i.e. the same coverage you get from Apple for the first year after you buy your Apple product, which of course is not the same coverage as AppleCare (f.ex. AC has phone support for 3 years, whereas you lose that in the basic warranty etc.).
Anyhow, I have not tested it yet, so I guess the proof is in the pudding. Only when I have the opportunity to test will we know the final truth.
But I did have work done under the AC. I had the hard drive replaced twice - once because it failed, and once under the Seagate recall. I also had the optical drive replaced twice. Every time, they came out to my place (because my iMac is on an arm, it's a hassle for me to take down), but obviously, if I have to have it fixed under the AmEx warranty, I'll have to bring it to be fixed, won't have the AC home visit perk.
We'll see. I've had it a little over 3 years now. I have 8-9 months of the AmEx warranty left, and by Feb 2014 it'll be 4 years old. Still happy with it overall, though it has its quirks - I don't know if everybody has this experience, but for me the biggest drawback is how it works with external hard drives hooked up; when my external drives go to sleep, any action on my iMac, even having nothing to do with external drives, such as firing up a random app is liable to give me multiple bounces - like 30 or so - until the external drives come back online... it's as if in order to do anything, the stupid iMac must fire up the external drives in case there are files there I might want to use (even if that's not the case because the app has no files there).