About transactions on mongodb To what extent can the atomic storage of MongoDB leave your database unsafe after inserts or updates on my data?

In other words: What are the possibilities of my data not been (inserted or updated) on collection?

Imagine a big application running, many inserts/updates and other things on the same time and asynchronous, I want know if that are a problem? What the risks to my data?
Copying Joao's answer (from question comments) so this Q can have an A.

No, there is no problem with that. Single inserts/updates are atomic and reads are always consistent. However, you don't have transaction blocks in MongoDB (executing multiple inserts/updates atomically). – joao Feb 24 '14 at 13:26