Replication does not always work if you deploy MongoDB as VM since master and slave instances may be running in a single physical machine.

Sure. And again, they make that clear. It's quite easy to find out that MongoDB doesn't "have single-server durability". If, like me (and at least one commenter here) you say, "what does that mean?", you can quickly find an explanation on their web site, or in many other places.

that's kind of like saying "we told you our parachutes won't open sometimes. well, not in our conference talks or in our marketing but it's on our wiki and we blogged about it".

if you want to see a message that is clearly delivered about (lack of) durability look at memcached. nobody misunderstands memcached's durability/consistency guarantees.

-Mikeal (after a few drinks)

Actually, it's more like saying, "we HIGHLY recommend having a backup parachute" (as, I'd imagine, most skydiving instructors would).

Also, I think I've always mention it in my talks.

I'm not sure how VoltDB escaped your wrath, it's an in-memory db that claims to be durable.

I went to the MongoSF conference. I found they explained it extensively in their conference talks.

I don't know about their marketing, but it's easy to find on the web site.