As he highlights, it is software it will likely have bugs
That's no excuse for the DB being buggy, but some of Mongo's problems are due to hard design constraints - it's not so easy to make a DB that is fast and reliable, and easy to configure. Other's are due to it being immature. Some of it is concerning - it seems it can crumble under heavy write load - not so great for a DB who's selling point is "fast at scale".
Part of Mongo's charm is how it works on a stock system. For traditional DB's, they cache stuff in RAM, then the OS caches the stuff they cached in RAM and swaps their cache to disk. Then you modify something, and the OS swaps the DB cache from disk to RAM, then the DB tells the OS to write the change to disk invalidating your OS disk cache, which then ... you get the picture. Mongo (and Couch) use the OS's cache, which is suboptimal on a tuned machine, but optimal on something you just threw together.
General rule for picking products -- if a product, by design is supposed to teach you a lesson about backup strategies, don't use that product.
I like Mongo because of its documentation. It's really really great. And good documentation = widespread adoption, and a team who actually cares about user's needs. What they really need is a lengthy tutorial on backups (which they already have written), linked from every page in their documentation. Because their reliability not something they should be hiding.
Why? Because they are making a database not an rrd logger or in memory caching server.
> What they really need is a lengthy tutorial on backups.
As I put it the grandparent post, as a general rule, avoid products whose mission is by design to teach you backup discipline. That is all.
> a team who actually cares about user's needs.
You know what is a better way to care about users' needs? Not losing their data because of a bad design. We are not talking about generating a wrong color for a webpage or even exceptions that are thrown and server needing restart, we are talking about data being corrupted silently without users noticing. Guess what, even backups become useless. You have no idea your data is corrupted, so you keep backing up corrupted data.