While I didn't buy this product from Amazon - it was £30 cheaper on another site - this is where I found it and I'm returning to mention just how good it is.
Firstly, the efficiency rating. Obivously this doesn't have any impact on the actual 'performance' of the supply, as such, but it's worth noting that a higher rating does draw less power from the socket, runs cooler, and shaves some money off the electricity bill. This is obviously rated platinum, which means it's rather efficient. So that's a plus. 80 Plus Platinum, in fact.
As you can see from the description, it's got a pretty hefty 12V rail so it's pretty much perfect for two high end cards, like GTX 680s in SLI, which is what I plan to use it for. It's obviously overkill on a single card system but I don't think anyone who's done any research would buy a >£150 PSU for that.
But by far the best feature is the hybrid cooling mode. It's not made entirely clear in the description how this works. Essentially the PSU operates without the fan running up to 30% of its maximum load, being cooled entirely passively and silently. But I've never heard the fan kick in, and yet it must have at some point because I've had zero heat problems with it. I guess the noise is just getting lost behind all the other fans. Whatever the case, it's great to have the low noise of a silent PSU combined with the raw power of an enthusiast-grade supply, especially since I'm coming from an older Corsair power supply with a noise level somewhere between desk fan and vacuum cleaner. There's even a 1000W version with the same cooling system for all you nutters out there.
One thing to note is that it's slightly longer than the standard form-factor for PSUs. This might be common in high grade equipment, I'm not sure, but if you're coming from the standard 150mm long supplies then take care. It blocked one set of screw holes for the bottom fan in my Corsair 500R case, which wasn't a problem because I don't use it.
Even if it might get in the way a bit (and comes with a ridiculous set of extras in the box. Seriously, the cables come in something that looks like a saddlebag with two velcro pockets, and the supply itself is sealed in a velvet-texture drawstring bag. That's all very nice, and I quickly repurposed the cable bag for storing a couple of DS's, but I wonder how much it added to the price), it is, in the words of one review site, 'the best power supply we've ever tested'. I can't speak for that, but I know it's the best power supply I've ever owned.