What about data persistence? Is it still enforced only through replication?

I really liked MongoDB's philosophy but this was the show stopper for me when I was exploring it. At least for some services I need to be certain that if the DB says it stored some data that really stored and not kept in volatile memory until it decides it's the right time to write them to disk.

It's been a while since I looked at it though, and that may no longer be the case. Are there any improvements in this area?