I’ll keep this short. Unraid was closed source, and development was painfully slow. The custom distribution of Slackware was pretty limiting, but mainly I switched because I finally came across something that could duplicate the functionality. Snapraid and mhddfs.
Snapraid takes care of the parity feature of Unraid and mhddfs handles the drive spanning. The best part of all this is that you can run Snapraid on pretty much any OS and mhddfs on any version of linux. So now I have an Ubuntu box setup with Snapraid and mhddfs. I’m exporting my media shares as NFS for XBMC and also am exporting as Samba for access from other clients. It’s also running the MySQL backend for XBMC, and it takes care of downloading my media. Basically, it is setup to do exactly the same things that Unraid was doing for me, but I now have total control.