Which NAS for Mac users?
I recently needed to replace an old NAS at home, and the cheapest option for my requirement was actually to build one and install FreeNAS on it.

You can add as many drives as your chassis will take, configure them to be RAID, mirrored, or independent, use UFS/ZFS on the partitions, and configure your shares as Windows, CIFS, or AFP with individual user accounts, groups, or getting permissions from an LDAP server.

Once you're set-up (which takes about 10 minutes from the CD) you're ready to go with a web interface which controls everything else.

While it's not HFS+, it is AFP capable out of the box so to speak, and works perfectly on my network with 2 Apple computers, and a Windows computer. It contains all of the resource fork information (meta data), and of course you can copy any existing data to it from anywhere else on the network.

Performance on a box like this is also going to be a lot better than most low to mid range NAS boxes too, which may be important with multiple users accessing large files. I backed up 580gb in just over an hour on a gigabit LAN connection.