Adrian Cockcroft of NetFlix proposed in a post last week the following use case:
He then posed several questions related to the use case and asked the NoSQL folks to answer how their database would solve the problem. 10Gen makers of MongoDB and Riptano commercial support organization for Cassandra responded.
Cockcroft's original post: Comparing NoSQL Availability Models
10Gen's Reply (via Roger Bodamer): NoSQL Netflix Use Case Comparison for MongoDB
Riptano's Reply (via Jonathan Ellis): NoSQL Netflix Use Case Comparison for Cassandra