Just my own .02 in regards to this.
After much debate (exclusively about price), I pulled the trigger and ordered a 5D3 on Thanksgiving evening, when bigvalueinc had them for 2886.06, shipped. My payment didn't go through until the following Saturday due to the holiday, and my original arrival date was November 29. That date came/went, bigvalue assured me they had them in stock and with US warranty (despite their growing negative feedback suggesting otherwise).
On December 1, I finally received tracking info that the camera was coming from Miami, Florida of all places! (I contacted some ebay members -- some received their cameras from NJ, some from FL). I received it today without a warranty card. The camera itself came in a kit lens box (lens removed) and was in tip-top shape.
As has been said already on the forum, I contacted Canon USA and they assured me that as long as I have the original receipt, they will honor the warranty (should the repair needed fall within its guidelines). So I'm pretty happy with things now, considering. Not trying to "spread misinformation," but I'm just going by what was told to me.
I'm not sure if this has been discussed, but as a sidenote, use caution should you purchase a warranty through Squaretrade. I did some research, and their warranty does not include accidental coverage (should you purchase through ebay or directly through them) specifically for the 5D3. There doesn't appear to be a way to include accidental coverage, either.
All told, I don't regret making the purchase (the price was too appealing) and I LOVE the camera. I just wish that bigvalueinc were a better vendor. Their customer service leaves a lot to be desired, and they are slow on the shipping (probably sold more than what they physically had in inventory is my guess). Word has it that they are a Grey Market vendor, so YMMV. It's a shame that all of their negative feedback seems to stem from the same issue(s).
For those who pulled the trigger for $2499, I hope your endeavors go smoother than mine did!
Not just any original receipt. From authorized dealer ONLY
Call them, and ask them how you get warranty service on a item that was a gift, and I had no bill of sale! I did. They said register it within 30 days, and include a note about it being a gift.
Canon knows the date of manufacture from the serial number, and will know if you send in a 3 year old 5d MK II claiming you just bought it. As long as the date of manufacture is reasonably close, they cover it.