howtoforge.com has uploaded a tutorial to boot a BTRFS filesystem on Debian
This tutorial will explain you how to boot from a BTRFS filesystem with kernel 2.6.31-RC4 and BTRFS 0.19. BTRFS is a new filesystem with some really interesting features like online defragmenting and snapshots. BTRFS is an experimental filesystem, use at your own risk. The kernel used is also experimental.
This tutorial worked fine for me but I don’t guarantee that this will work for you, and decline all responsibility for any problem you might have.