It has been about five months since the release of Btrfs 0.16, but version 0.17 has arrived to bring the Btrfs programs in-sync with the file-system's kernel module. The disk format for Btrfs is now believed to be stabilized and will not change unless the developers encounter any "critical issues" now that there should be greater testing of this file-system with it being in the Linux kernel.
Version 0.17 of Btrfs brings transparent zlib compression (available through a mount option), improved block allocation routines, improved block sharing while moving extents, and seed device. Besides those prominent changes, there are also other bug-fixes and performance improvements in this newest Btrfs release.
Originally Btrfs 1.0 was expected to be released in the fourth quarter of 2008, but now it looks like that point won't be reached until some point in 2009. The Btrfs change-log can be found on their Wiki and the v0.17 release announcement can be read here.