I haven't tried that. Just got an AWS account, though. Their storage solution looks interesting ($0.10 GB).

Have you read about Spot Instances? You can set a maximum hourly price that you're willing to pay in order to keep your server up. The "ask" price from Amazon fluctuates with supply and demand. If the BitCoin app could be made to save frequently and recover from downtime quickly, you could set your spot price to something that you know will make you profitable.

Just set your maximum bid price to:
(max bid price) = (blocks hour) * (coins block) * (USD coin)
Where blocks per hour is how many blocks you expect test to generate in an hour. That's the only tricky part of the equation.

Until recently, the "ask" price for a m1.small instance appears to have been hovering around 2.9 to 3.1 cents USD. There was a somewhat prolonged spike to 6 or 7 cents lately, but that might not continue. At an average spot price of $0.03 hour and an exchange rate of $0.0041 Bitcoin, you would need to generate one block every 6.8 hours, or 3.5 blocks per day. Is that unreasonable? Probably, but I'm not sure how fast a m1.small instance is. Also, that assumes that your instance is generating blocks for every moment it is up, which isn't true, since the instance has to reload and restart every time it goes down. On the flip side, Amazon doesn't charge you for partial time if you get shutdown (or perhaps they don't charge you for the ENTIRE hour -- it's a bit unclear).

It's an interesting idea, and might work well for you.

By the way, how did you get a metric on how many hashes your Mac checks per hour?

I have access to a couple of VPS instances running on Xen that often have a LOT of spare cycles. Since the only thing I'm billed by usage on is bandwidth, I might as well get my money out of the things.

The cheapest one I have is $8 month. They don't give any good info about CPU strength (and are generally unreliable), but at that price you only have to generate about 1.3 blocks a day, or one every 18.5 hours. That's still a bit high, but even if I only make $4 a month, that's a nice dividend since making BitCoins isn't what this box is primarily all about.

I have not personally mined from AWS, but faced one situation in our project where one of the project member committed the public key into github and next day we get a call from  AWS saying our account has been billed like 1500x times the normal billing. There was no AWS administrator in our firm till that time and this leaked key was used by the hacker to create hundreds of spot instances. This has been used to do the btc mining, we terminated all the instances as soon as we got it. Not sure how many they managed to get, but the way so many instances were created, i feel if we are like getting a good mining to happen, we may need to invest heavily.