Please, be careful with this new kernel, I have suffered from multiple fs corruptions. Give a look to:
http://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg38092.html http://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg38039.html
It seems that the bug is already identified, so a fix will land soon. Great news!