Earlier quoted context omitted.
As I would put it: In the event of a single server crash, Mongo may need to be restored from backup, or another master. CouchDB handles this much better, and can just restart where it left off. But in the worst possible single-server scenario, there's smoke coming out of your server and the hard drive is toast. CouchDB and MongoDB perform about the same - if you had replication or a recent backup, you are fine. If yo…
If you are running with journaling enabled, you should get a much stronger crash recovery case. In the event of a crash, the journal will be replayed: http://www.mongodb.org/display/DOCS/Journaling
And that is a good feature on a database to have! Why not make it the default?