I've heard about btrfs being "just around the corner" for a good while now. ZFS on Nexenta and even FreeBSD is pretty robust. It's a great storage platform. I wouldn't let waiting on a stable btrfs make my SAN/NAS decisions for me.

The other concern in that realm is that when you're centralizing storage concerns to lower costs, boost performance and increase reliability you don't want software issues or corruption to take down your entire business.

ZFS can be a painful enough learning curve when it comes to that environment. I wouldn't trust btrfs until it's been stable for a couple years there. And outside of that environment, there are plenty of good stable alternatives for the DAS space. While ZFS is nice there, and I'm sure btrfs would be as well, that's not the bread and butter for these systems.