Differences in use case for Column and Row-Oriented Databases.
Column-Oriented Databases are best used for analytics against large data volumes. Row-oriented Databases are best suited for transaction processing with low-complexity, high-volume datasets. NoSQL databases are best suited for high-complexity, high-volume datasets.
Source: The emerging database landscape
Les différentes implémentations des bases de données NoSQL / Les technologies Web et les tendances à surveiller en 2011 (via rtrillard)