OS X FileVault is the equivalent to a black hole for your data. Nothing else has ever caused as much data loss for me as FileVault has. It has the habit of turning your files into 0 Bytes sized file system entries whenever disk space is low or you should have to reboot without logging out - like after a crash or lockup. Which happens dozens of times a day if you’re writing a kernel driver...

 

So, if you really really need to use FileVault, you better have a highly paranoid backup strategy.