This is something I have been waiting for. I was already utilizing Amazon S3 for heavy storage of files, images, and large text blobs. I use MySQL or Microsoft SQL Server for most back-end databases, however 90% of the time I am using only about 10% of the capabilities available to me.
I am looking to add, update, and delete text and numeric data is very small amounts most of the time.
SimpleDB is perfect for this type of small to medium size web site and application deployment.
I am excited about playing around with it more and see if it can become the perfect scalable database platform that I have been looking for.