A nice article about scaling in general and scaling relational databases can be found here:
http://adamblog.heroku.com/past/2009/7/6/sql_databases_dont_scale/
SQL databases are fundamentally non-scalable, and there is no magical pixie dust that we, or anyone, can sprinkle on them to suddenly make them scale.
May the future of NoSQL (or better NoACID) databases be bright …