Amazon announced a new AWS feature called Lambda. I watched the presentation with great interest, however, I did not make it all the way through... even at 7min it was too long. The idea is simple. Some event that your code is configured to watch occurs. When it occurs your code starts running until it finishes running and then stops.
This is an amazing bit of architecture, design or implementation. Whatever you want to call it. In many respects it borrows from flow based programming without actually saying it.
Pricing - there are three factors that contribute to the overall cost.  the number of requests,  the running time of the function,  the amount of memory you opted for when configuring your function. I assume that amazon is normalizing the CPU over the function in order to calculate some sort of compute index.
If I were to run my function non-stop for the span of the month then the cost would be just under 6 dollars. (2.6e9 / 100 * 0.000000208) and if you get the upper bounds of memory - 1M - then you're looking at $43... if you run you app non-stop... 24x7.