I finally got around to playing with Amazon's EC2 yesterday, just going through the basic tutorial. Pretty much as I expected, it was trivial to create and start a new instance, although I could see getting tired of keeping track of the access identifiers for command line usage and wanting to find a GUI such as RightScale, which will even automatically launch new instances to deal with increases in demand on your site.
The idea of being able to quickly add extra compute power, and only pay for it when you need it is quite appealing. Many web sites experience significant peaks in their business and could potentially save on infrastructure costs with such a model. For example, at my last gig we designed systems that had to deal with peak traffic that was more than twenty times the average for just a couple hours at a time, requiring a significant investment in hardware that went largely unused most of the time. It's also nice for companies just starting out that don't have a firm grasp on their hardware requirements yet.
I do wonder how well Microsoft can play in this new space given their server-centric licensing model. If I want to have a hundred servers on standby, how would I license Windows for that? Some quick Google searching for "windows cloud computing" turns up some information on a future cloud-centric operating system called "Midori", a beta offering of Microsoft Online Services, and even references to Windows Live. But this wouldn't help me deploy a .NET application to the cloud today. This fairly recent post on ZDNet echoes my confusion, and adds even more concepts. Red Dog? Microsoft appears to be playing catch up again with respect to understanding the Internet.
Regardless, I want to start taking advantage of cloud computing. Even if it's not yet ready for mission-critical applications, one could start by moving certain workloads into the cloud, such as load testing or compute-intensive batch processing. I don't know of any other way I could start up a server or two and play with them for an hour for just $0.25.