For our startup the ability to scale up and down on instances is what makes Amazon great. We often run just 4 instances, but ramp up to 10+ at times when we're

For our startup the ability to scale up and down on instances is what makes Amazon great. We often run just 4 instances, but ramp up to 10+ at times when we're busy. This dramatically reduces the cost of having hardware which is underutilized. Not sure of anyone else doing anything similar - is there?