Freenas using generic hardware
I love the ability to grab an old computer, fill it full of cheap hard drives, and install Freenas on a CF card or USB drive. Software RAID is reliable.
A key point, if any of the hardware dies, the RAID array can be rebuilt when the software is installed on new hardware, unlike some proprietary solutions (NAS or RAID cards) where you may be tied to a particular vendor and/or model, which, after time, may not be sold/available.
Works fine with Macs and PCs -- and for this reason i use SMB shares rather than AFP. Performance is fine.
I use the SMB shares to stream to all the computers in the house, and there is no problem.
Time Machine backups are a little more complex, involving creating a Sparse Bundle (which is not the official method). For this reason, i don't do this, i use Carbon Copy Cloner to run to a disk image (dmg) every night.
I use MediaRover to sync iTunes libraries, and this works fine. Other iTunes support is available (an iTunes/DAAP server called Firefly), but i haven't used it.
It has a BitTorrent server built in, but again, i haven't used it.
Administration is very easy (web based), setup is not difficult, but there are several steps to add disks, format them, create a RAID array, create a mount point, enable the services (AFP or SMB) to access. Documentation and community support are satisfactory.