We’re seeing a lot of NoSQL adoption, mainly because it performs better in terms of read/write latency and can also scale much more easily than traditional relational databases. They are also super flexible to develop with. They are schema free, which means their data models can evolve and grow, as they need to. They provide an agile data model for agile developers who want to do things faster without being constrained by the schema limitations of relational database technology. That said the relational database isn’t going away, its still needed for atomicity working with middleware like XAP. NoSQL is more about Not Just SQL than saying bye bye to relational databases. We’re specifically seeing NOSQL in e-Commerce retail, social networking and even Telco who are looking to migrate to Cassandra for example for better throughput and performance from both an OSS and BSS perspective. If you look at the needs of Telco customers they want real-time Business Intelligence of their customers so they can provision relevant content on the fly to try and maximize their interaction with customers on their portals. They can’t get this BI with traditional relational databases and monolithic application architectures; they simply don’t scale or perform quickly enough.
All good and valid reasons: better/predictable read/write latency, development agility, schema free.