I'm running 9.1 with a slave using streaming replication. A coworker wants to turn off fsync on the master and insists that the slave will still be in a usable state if there is a failure on the master.
This would only be safe if you made sure to shoot the master in the head after a crash. If the master ever comes back up again, through automatic recovery or through start-up scripts, it could start feeding corrupt WAL records to the slave, corrupting it as well.