I've been trying to sort out the cashback deal and have had probelms.
First thing to be aware, if you buy online through Amazon, Olympus told me that only purchses directly from Amazon are valid, so not through Amazon Marketplace.
Secondly, having bought my camera from Amazon (which should qualify), I have sent them 2 documents as proof of purchase, neither of which have been accepted:
First I sent a copy of the order confirmation Amazon emailed me. Olympus didn't like it.
Then I dowloded a copy of what Amazon called a receipt and sent a pdf of that to Olympus. They haven't accepted that.
I have emailed Olympus to find out exactly what details they require on the "receipt" and await a response.
I am also awating a VAT receipt from Amazon ... which they can only send via fax or as a paper copy via the traditional post.