I use it as my default file system on FreeBSD. It was rough in FreeBSD 7.x (around 2009), but starting with FreeBSD 8.x it has been rock solid to this day. The only gotcha (which the documentation warns about) has been that automatic block level deduplication is only useful in a few special applications and has a large main memory overhead unless you can accept terrible performance for normal operations (e.g. a bandwidth limited offsite backup).