For which projects did use NoSQL databases and for what kind of problems?

It is hardly possible to name a project for which a NoSQL database would be useless, except for a blog or a home page. As the main use cases for NoSQL stores I would mention the following tasks:

● collecting and analyzing large volumes of data
● scaling large historical databases
● building interactive applications for which performance and fast response time to users’ actions are crucial

The major “drawback” of NoSQL architecture is the absence of ACID engine that provides a verification of transaction. It means that financial operations or user registration should be better performed by RDBMS like Oracle or MS SQL. However, absence of ACID allows for significant acceleration and decentralization of NoSQL databases which are their major advantages. The bottom line, non-relational databases are much faster in general, and they pay for it with a fraction of their reliability. Is it a good tradeoff? Depends on the task.