I have used MongoMapper for awhile but decided to migrate to MongoId. The reason is hidden issues plus arrogance towards users. I had to jump through hoops to make MongoMapper work with Cucumber (succeeded in the end) and to put a couple of patches even the project was simple, but it’s not the point. When I tried to submit a bug fix (due to incompatibility with ActiveRecord), they seemingly got pissed off that I found a problem and I was pushed around. While I was testing, I also encountered a major bug with their query implementation, while their testing was tuned in a way that the tests pass. After my previous experience, didn’t dare to submit it.
They have a significantly lower number of pull requests and bug/feature submissions than MongoId, i.e. community participation is much lower. Same experience as mine?
I don’t know which one has more features right now, but I don’t see much future in MongoMapper. I don’t mind fixing issues and adding functionality myself, but I do mind situations when they wouldn’t fix bugs.