Neat article. It does not directly talk about cost implications though. When I started my company, we chose Google Big Table thinking of scalability and other goodies that were promised. But as we started scaling the price of the database spiralled out of proportion!

Next, we went to AWS. We started using RDS and now we realize we cannot reduce the storage so we end up paying for the disk size although we now use much less. Moving TBs of data is such a pain on RDS.

Still looking for a better DB solution!