I remain very enthusiastic about Google's AppEngine (and also I am very much enjoying my developer's Wave account). That said, Amazon's AWS services are having a much larger effect on my work for customers and my own work and research. AppEngine is great for some types of projects, but EC2 can be used for anything.
I have a text mining experiment that have been planning for a while, and today I have some free time to start setting it up. I have 3 old desktop computers (with a reasonable amount of memory and disk) that I usually haul out of my closet, run "headless," and set up for text mining and machine learning projects. Although I own these boxes, there is a drawback to leaving them running for several weeks in my home office: noise, heat generation, messing up my work environment, etc. I did a quick calculation and estimated that if I instead use one EC2 instance, a reasonably large ESB disk volume, and Elastic MapReduce when I need it to make Hadoop Map Reduce runs, the cost over a few week period is a small business expense. Anyway, I am setting up a work environment on an EC2 instance "as we speak."
My wife and I often evaluate what we really need in our home (we like to keep our small house tidy and elegant) and I would like to get rid of old computer hardware that I can do without - and, in the USA, our schools are poorly funded so contributing old hardware to our local high school with the latest Ubuntu installed could be a good thing.
Note: I would like to thank Amazon for providing a grant to me to cover my EC2, S3, and Electric MapReduce expenses for writing my last Ruby book's examples and permanently providing a MCI with all of the book's examples.