The filesystem disk format is no longer unstable, and it's not expected to change unless there are strong reasons to do so. If there is a format change, file systems with a unchanged format will continue to be mountable and usable by newer kernels.
The Btrfs code base is under heavy development. Every effort is being made to keep it stable and fast. Due to the fast development speed, the state of development of the filesystem improves noticeably with every new Linux version, so it's recommended to run the most modern kernel possible.
For benchmarks, it's recommended to test the latest stable Linux version, and not any older. If possible, it's also recommendable to test the latest Linux development version. Also, it's recommended to test the different options, f.e. different compression options.
Newly added features may need a few releases to stabilize.
If you have any bug, problems, performance issues or questions while using Btrfs, please email the Btrfs mailing list (no subscription required). Please report bugs also on Bugzilla.
Szerintem a no longer unstable != production ready.