yes, we are using mongo from 1.6.3. Reliability, Locking and Data security (not losing data) are never first priorities on their to-do list, they just push new features and busy doing marketing propaganda about how web-scale mongodb is(which is fake). I submitted a jira issue about losing data when sync a slave, it's already 3+ months, all they did is let me try the new releases to see if it fix the problem. I tried the latest 2.0.1 release, and it's still cause data loss. Every time I sync a new slave, I pray to god, hoping not lose data.
How come a DB lose data so frequently and it sill call itself web-scale? It just breaks when you need scale!
For auto-sharding it's also super unreliable, tried once and it failed, and now we are using a lib that do application level sharding. We are also considering move to other databases that at least know not losing data is the first and most important thing of a DB.
Some one summarized the issues of mongodb, http://pastebin.com/raw.php?i=FD3xe6Jt , we experienced most problems in the article. So just a remind for someone who want to create serious product using mongodb, read the article, it's not FUD, it's just so true that I hope I read it 1 year ago, so we don't have to try moving so much legacy data to a new database solution.