btrfs is considered experimental and unless you're very adventurous, you should avoid using it. There is neither a fsck tool available in case the
btrfs filesystem becomes corrupt (after a power failure for example).
An excerpt from the release notes:
The btrfs filesystem is considered experimental in this release. It can generally be installed and used, but with a number of problems. You should only use it if you are comfortable with dealing with problems and helping us resolve them.
- As the btrfs wiki notes: "Note that Btrfs does not yet have a fsck tool that can fix errors. While Btrfs is stable on a stable machine, it is currently possible to corrupt a filesystem irrecoverably if your machine crashes or loses power on disks that don't handle flush requests correctly. This will be fixed when the fsck tool is ready."
- GRUB cannot detect a btrfs installation within an encrypted disk, and fails to set up the correct kernel parameters. (757631)
GRUB can actually boot from btrfs filesystems (instructions), but note that Ubuntu still consider btrfs as experimental.