[pavanky]

6Gigs on a single GPU is very tempting. And the single precision performance (Theoretically 2.2 TFLOPS) per GPU on the K10 is more than anything else you can get on the market. To buy one of those would cost you $3500-$4000. To buy two + motherboard + xeon would probably cost you close to $10,00. If you want to scale it and set up a cluster, the cost per machine scales up and the amount of man hours spent would become a factor.

Amazon offers a heavy usage deal which comes out to ~ $11,000 per instance if used 24x7x365.

You could argue that the cluster / machine you set up would be useful for more than a year. This is true to an extent, but at the current rate of development GPUs become obsolete rather quickly and suddenly having a cluster on the cloud sounds more appealing than going through the process of updating your machines every 18-20 months.