MongoDB has been getting lots of mixed reviews on Hacker News.
I also have had a particularly poor experience with MongoDB...
A few months ago, I met some nice people from 10Gen. They gave me a a MongoDB mug.
Now after moderate use with a high quality brand of tea (http://www.barrystea.ie/) and a industry standard version of a dishwasher (http://www.siemens-home.co.uk/our-products/dishwashers.html) there have been some disturbing results:
The data stored on this mug has started to fade away badly. If this is what happens to the data I can see - what about all the data in the database? Worse again - no errors were thrown (I'm running in default mode)
Fearing the worst I migrated our corporate MongoDB instance to a etch-a-sketch stored in a vibration proof room.
I know I could have raised a bug about this or tried to get some support but a long blog post and a quick over-reaction is a more pragmatic approach. At the very least 10Gen could send me a new mug.
So if you are still using MongoDB - YOU HAVE BEEN WARNED...