Actually, I feel that these are some of the reasons that I find MongoDB to be an attractive solution for certain purposes. You can give up some facets of durability and make up for it in ease and performance. MongoDB actually fits quite well into various web apps that have a need for a secondary, non-authoritative datastore that needs to be highly available but not as reliable. Any kind of real-time stream feature would probably benefit from this. Just keep an authoritative copy of your data in your relational datastore of your choice, and asynchronously replicate data as needed to MongoDB. Since it's a non-authoritative datastore, you can denormalize it as much as you need. Works pretty well, IMHO.