I use it for offline operations since we only have a single overloaded MS SQL database server. So i sync the data to my local mongo instance creating documents

I use it for offline operations since we only have a single overloaded MS SQL database server. So i sync the data to my local mongo instance creating documents with only the fields that i need. And i have scripts written to do analytics and partition the data to reveal patterns and generate reports and so on. It's very fast and the flexible schema makes the code much more flexible and easy to write. And did i mention it was fast? You should definitely give it a try and consider using it for such systems. My only issue with it is that i am running it on a 32-bit system and so i'm limited to 2GB a database.