I've been using btrfs in my laptop on my OCZ Vertex LE [0] since that drive was shipping with the data-eating v1.0 firmware. [1] I'm also running it on my desktop, and in a force-compress multi-device firewire-attached configuration for a multi-TB Postgres tablespace. It has been many, many years since I've run into a data-loss issue of any kind, despite unexpected power-downs or other failures.
Now... if you're using Kubuntu 15.04[3], with btrfs as your root volume, know that system lockups that require a hard reset may well do something to the log that makes mount hang. Do this [4] if your "task is hung" backtrace looks something like the one in the wiki page, then btrfs-zero-log is the thing you need to do.
[0] The drive is still going strong and error-free, too! :D
[1] This drive is what taught me to ALWAYS upgrade the firmware in your SSDs, ASAP. :P
You can follow the btrfs mailinglists to see the stream of people coming in that hit a case where btrfs can't recover by itself. I've hit one myself that required a btrfs-zero-log "fix", but I'm not running Ubuntu.
You have been extremely lucky. Keep making backups, though.
Now... if you're using Kubuntu 15.04[3], with btrfs as your root volume, know that system lockups that require a hard reset may well do something to the log that makes mount hang. Do this [4] if your "task is hung" backtrace looks something like the one in the wiki page, then btrfs-zero-log is the thing you need to do.
[0] The drive is still going strong and error-free, too! :D
[1] This drive is what taught me to ALWAYS upgrade the firmware in your SSDs, ASAP. :P
[3] Christ, what a nightmare this version is! :(
[4] https://btrfs.wiki.kernel.org/index.php/Btrfs-zero-log