IMHO, extended warranties are not a good investment.
You should only insure against hazards where you cannot afford to repair/replace the item. Otherwise you spend a lot of money on insurance premiums where the likelihood of anything going wrong in a catastrophic way is low.
I bought an extended warranty for my first DSLR -- the D30 -- wondering how durable it might be.
I felt like a chump after I held the camera and then realized unless I dropped it or got it wet, anything that was lkely to go wrong was likely to wrong during the warranty period. AND, if I dropped it or got it wet, they were not going to cover it under the warranty.
I have own a D30, a D60, a 10D, and I own a 1Ds MkII and a 20D. I am so obsessive compulsive, I have been able to sell every camera LNIB. Not a scratch or a mar. When I have slipped or fell (it goes with nature photography), I have taken the shock. The camera has never hit anything by my too large belly. I have contorted myself a time or two, just to make sure I protect my cameras.
I think most of us are mindful while we use such expensive equipment out in the field. Photojournalists can be rough on gear sometimes, but that comes from a newspaper paying for the gear. Anyway, I know of no one with a 1Ds MkII, 1D MkIIn, 5D, etc. who is careless with their gear.
If you are careful, you can expect serious manufacturing defects like faulty components, faulty assembly, etc. to appear during the warranty period.
Admittedly, I am talking about my experience and the experience of a few people. Perhaps others reading this forum will relate other experiences. That's the risk when we generalize from a few experiences.
Cheers,
Mitch