Well, I just purchased a 70-200 f2.8 IS and a 100-400 IS 2 weeks ago not knowing if and when the rebates would actually happen. My reason for buying was to do it before the price increase. Guess what....the price on the 70-200 is now $30 less on the site!
Yes I will call and ask for the reduced price and about a credit for the upcoming rebates ($100 + $125 = $225). That kind of money makes it worth my while to make a couple phone calls. I have nothing to lose.
I have read several post here and other forums about this same issue. Not having any experience personally with Amazon but from what I have read, Amazon is very consumer friendly on matters like this. The way to work around this is simple. Claim buyers remorse within the 30 day return period then repurchase the same item at the reduced price from the rebate.
Just my 5 cents worth.