But... still. I decided to go benchmark, because I don't like saying something sucks without good cause.
Let's say we're interested in a few NTLM length 8 passwords. Fairly standard for a corporate audit.
I know, I know - glacially slow compared to "modern hash cracking rigs" - but how much does it cost to do?
Well, at 3B hashes per second, length 8 (95 characters) will take 615 hours. At $2.10/hr standard GPU instance pricing, that's nearly $1300! Ouch! You're really better off buying a 6990 or something at that price!
But what about spot pricing? Amazon clearly isn't having them heavily utilized, because their spot price is $0.346/hr right now. And that, my friends, works out to $213. Which is a whole lot more interesting - especially since that's the total cracking cost, if you use one instance and a month, or a bunch of instances and a lot less time.
Just something to think about...
Updated July 31 2012
If you are looking to actually do this, http://blog.cryptohaze.com/2012/07/installing-cryptohaze-on-amazon-ec2-gpu.html has links to the scripts to do so. And the speeds are even better, making the cost less!