Yes, if people are sing MongoDB for applications requiring ACID, it is probably not the best fit. However, there are many great use cases that MongoDB is a great fit for, sometimes characterized by needing a lot of read slaves for complex analytics, where data loss is not a lose-the-company proposition, rapid prototyping, etc. I just ported a Java GWT + Objectify appengine application to run on an EC2 with MongoDB and it was shockingly easy to do. Also, you an give up some write performance for increased data safety.
MongoDB (along with PostgreSQL, RDF data sotres, and sometimes Neo4J) is solidly in my preferred tool set.
MongoDB (along with PostgreSQL, RDF data sotres, and sometimes Neo4J) is solidly in my preferred tool set.