I run FreeBSD on a microserver with 4x3TB in raidz1, and it was simple enough to set up, and NAS4Free is even easier. I believe it's supported time machine for a long time, though it'll be the annoying disk image based time machine (same as used on the time capsule). It'd be really nice if there was a nice way to do timemachine backups and use ZFS's snapshots. I'd love to see rsync with this ability without needing to write a script to form the snapshot after the sync.