Meh, I played around with FreeNAS for a while. I originally thought it was neat, but I kept having problems with it and eventually realized that it was easier to just set everything up myself. The GUI didn't offer that much in the way of ease of use. A short list of my observations.
1) FreeNAS makes it dead easy to set up ZFS...but ZFS is actually pretty easy to setup on its own. Easier than RAID/LVM by far. So no huge gain there, in my opinion.
2) FreeNAS makes it so you don't really have to learn the ins and outs of FreeBSD, but zfsonlinux is fairly mature and works well, so not a big deal for me.
3) This may be my linux bias showing, but FreeNAS is limited by the capabilities of FreeBSD. Hardware support is the biggest one (controllers, nics, etc). For example, plenty of Dell hardware won't work optimally. Also, what the fuck did they do the PAM? Lots of functionality missing (kerberos password changing, mkhomedir, etc). The version of SCP seems to come from a stone age that doesn't know about directory recursion. Just lots of little things that really annoyed me. No NFSv4 support. Seriously, this is like 10 yrs old now, and you still can't authenticate NFS users over Kerberos if you are using FreeNAS. Maybe it is fixed in this version, but not in 9.2.
4) Some aspects of the UI were nice (ex: being able to easily to see appropriate ZFS flags) and other not so nice (ex: the snapshot interface). Yes, FreeNAS supports the ability to replicate ZFS, but this requires a cumbersome setup that even involves saving your ssh private key into the UI (maybe they have changed this since then). It's easier to just set this up in a cron job on your own, in my opinion.
5) FreeNAS makes some things very easy, but if you need to do anything differently, it's a pain to work around the UI. The settings are saved in a special database that writes config files on the fly, so you have to know what to edit to make a change. I spent a lot of time making FreeNAS talk to our domain controller and enumerate groups correctly, because the UI had a generic way that didn't work with our schema and there was no way to just change the necessary settings.
Bottom line: if you want to get a quick NAS running to use as a media server, FreeNAS works pretty well. But if you have special hardware or integration needs, you can probably achieve everything you need much easier by just configuring everything by hand.