I haven't personally used it but I believe there is (was) enough factual technical information to reach this conclusion, including this linked blog post of Kyle's. I was shocked when I read that. Data loss is generally not okay and expected. I'd say most were not aware that the potential for data loss was actually in the design of these products before the Jepsen posts. I believe these flaws impacted most of what people were using it for, so its continued use, particularly on new projects, in the presence of other databases such as Cassandra and Riak is surprising.

And this is not even factoring reports of slow progress, in your face bugs, and PITA manageability.

While it us true substantial progress may have occurred in the less than two years since that test, I would need to see some solid evidence of substantial improvement to consider mongoDB.

That's my outlook based on what I have read.