One new package has been added in testing/ directory which is btrfs-progs that consist of btrfs-convert. It's a conversion tool which can be used to convert ext2 to btrfs filesystem. If you need to convert from ext3 or ext4 to btrfs, please have a look on this wiki page.
This filesystem will be used as a default filesystem in some of the future release of other Linux distribution, namely Fedora 14 and Ubuntu 10.10. It's gaining some popularity, so i guess Slackware 14 might have a chance to support this filesystem as well in the future