Amazon's SimpleDB online data storage and querying service is now in unlimited public beta, which means that you can sign up for the service and have your account activated immediately. Previously, new users had to wait an indeterminate amount of time until they were granted access to the limited beta.
Amazon has also changed the service's pricing to encourage people to try the service and stick with it. Moderate usage of the service will be free for at least six months for up to 1GB of data, while the ongoing data storage costs beyond 1GB have been slashed from $1.50 to $0.25 per GB/month.
Finally, a new DomainMetadata API operation will be made available for retrieving statistics about a domain ("database" in SimpleDB parlance) such as the total number of items, and the storage consumed by all of your attribute names and values. ~~Unfortunately the link to the DomainMetadata API documentation link is broken as I write this, but full details are available in the PDF version of the Developer Guide.~~ The DomainMetadata API documentation is now available in both HTML and PDF versions of the Developer Guide.