I have been using NAS4FREE for several years now and have found it very stable to use.
There was one issue that came up recently with the web GUI and the guys at NAS4FREE were very quick to fix it.
I trust it with all my data and most likely will for a very long time to come
Great stable NAS distribution, and in a lot of things performing a lot better than FreeNAS where they do use users as freenas often uses test code without users do aware. Also NAS4Free code base exist way longer and they did not need webgui rewrites over and over again.
With NAS4Free you have a great NAS system, it's a shame some die hards only tell you to use FreeNAS over and over again but do not say to try NAS4Free too. NAS4Free is what FreeNAS ever was.