I've been working for a while to migrate all of my data to my raidz box off of my mythtv box itself - which I finally completed this week. I've been planning to rebuild the system using software RAID, so getting all of the video data off made things much simpler (instead of the ultracrappy LVM setup I had previously - basically, I had appended 2 400 GB drives together as a workaround for my limited storage).
Once everything had been rsync'd over to my Solaris box, the process of actually rebuilding and moving to software RAID was pretty painless. I'd made the rsync backup using an LVM snapshot when the system was live, which worked really well. Rebuilding the system using a gentoo live CD only took about an hour, and everything is working fine.