SQL Server Data Services (SSDS) are highly scalable, on-demand data storage and query processing utility services. Built on robust SQL Server database and Windows Server technologies, these services provide high availability, security and support standards-based web interfaces for easy programming and quick provisioning.
From : Main SSDS Site
InfoWeek: InformationWeek Site
Detailed Blog with Info From Mix08
Query Syntax – Etc
A Bit More
http://dev.live.com/blogs/devlive/archive/2008/03/12/220.aspx