Upload & Sell: Off
Thanks everyone for your help. I bought a 600EX from Overstock.com, here in the United States, for $488. It shipped from New Jersey, and the product info on the website talked about the wireless capabilities, 1 year warranty, etc.
When it arrived, to my surprise, it was a 600EX, not a 600EX-RT. I know Canon sells the 600EX overseas, but they don't in the U.S., so I'm pretty sure there would be no warranty. There obviously also is no wireless capability.
In light of this, $488 was not a good deal, and I'm just returning it to Overstock.com instead of replacing my 580ex II with it, or trying to sell it new. I guess it is possible that Canon is now selling the 600EX in the United States, but I don't see anything else supporting that, and I therefore think it is more likely that Overstock.com is selling imports.
Thanks again everyone.