[jdrobins2000]

I agree that Cassandra CAN be used for basically everything a RDBMS can, but to claim it can be used just as easily is a stretch (based on my experience migrating from PostgreSQL to Cassandra). It lacks many administration tools, and for data with complex, non-hierarchical relationships, data modeling is more complicated and you must do any joins yourself. Sure you can get major performance and scalability gains if you use it correctly, but you also give up being fully ACID.

As a developer, using C for all data in any complex application is going to be harder up front than using a RDBMS. From what I have heard and learned about C, though, it is less painful to use C for a highly performant/scalable database than trying to scale most or all RDBMSs. From what I have read, Mongo is also hard to scale.