Since I joined a Big Data Event : Frankfurter Datenbanktage 2013 - I started to take also a look to non-relational technics too. The RDBMS is not for every asepct the correct and fitting and fulfilling answer to all data related IT challenges.
Frequently I wondered about how facebook could handle such an dramatic amount of users and data growth. I found an interesting presentation from the facebooks HDFS - Development-Lead Hairong Kuang optimizing HDFS (Hadoop DFS) for Scalability, Storage Effiency and Availability.
An RDBMS would not scale to that amount of load - reasons for that is the explained in theory with the CAP-Theorem which I will post about later;
Now to the presentation on InfoQ : http://www.infoq.com/presentations/Hadoop-HDFS-Facebook