I planned on getting that brick of a card, tossed it up against the MSI GTX580 lightning, but atm i'm leaning towards getting a lightning. my reasoning being
1. it's a triple slot card, so unless you've got no plans to SLI, or have a very big motherboard with a good layout, that size is going to cause a problem.
2. It performs on par with the Lightning (the lightning, apparently, overclocks better, but the Matrix is quieter and-in-some-cases cooler too) but the Matrix is anywhere between £20 and £100 more expensive depending on the vendor...a lot of that extra cash is probably due to the ROG branding. See : The Mars II price vs performance.
3. ASUS are not known for their brilliant customer service.
Other than that...Its a sexy, sexy GPU. That is undeniable. Hell I'm not even sure at this point which i'd like.