MongoDB has a great story around big data and horizontal scalability, but it is also a great general-purpose database and often the right choice even when you don¹t have a lot of data. I gave a talk at a local San Francisco NoSQL meetup about this very topic. The talk received a ton of good feedback - maybe I'll give it again!
Here are the slides:
http://www.slideshare.net/willshulman/mongodb-its-not-just-about-big-data
Enjoy!
