I ordered a Canon 580EX II and a WFT-E3 on Sunday evening. Both were in stock at the time and I got the full 30% off my invoice value. The goods were delivered today and I've checked them out and everything seems pristine and in good working order. Total net cost was £618, with £40 yet to come from Canon as a cash back for the 580EX and a further £39 tracked with Quidco. It remains to be seen whether that gets paid successfully, but I don't see why it shouldn't. Best price on Camerapricebuster for these items would be £824 before any cash backs.
By the way, given the concerns, I did drop a note to my credit card company and they assured me that if the card got charged and the goods failed to show all I'd need to do is to file a dispute.
I'm now going to see what other goodies I can find, while stocks last.