Chris shares that the Btrfs file-system is currently working against the latest kernel Git tree and not much has changed with this file-system code since early December. The kernel mailing list thread goes on with further technical discussions of Btrfs. Though whatever may end up getting merged into the Linux 2.6.29 kernel will likely be deemed experimental.
Originally a version 1.0 release of Btrfs was expected in the fourth quarter of 2008, but that did not take place. The last development release of Btrfs was v0.16 in August. When any further activity takes place, we will be sure to let you know. We will also be delivering benchmarks of the Btrfs file-system in the near future. The Git tree for Btrfs to build as a standalone Linux kernel module can be found here. Additional information on this file-system is available here.