Most of the devs seem to be of the opinion "we don't use it so we have no opinion", or there wouldn't be horrifying bugs in it over 3 years old.
That said, very few if any of them have involved actual irrecoverable data loss versus just requiring lots of handholding to get your data back.
edit: I suppose at the point where I'm being quoted on HN about this, I might as well link my list of encryption bugs.
https://docs.google.com/spreadsheets/d/1OfRSXibZ2nIE9DGK6sww...
I still need to add a couple of new bugs, but almost all of them are dupes or related to one of two flaws - a narrow race in the ARC (...probably), where you can sometimes NULL dereference for fun and sadness, and zfs change-key and send -i resulting in the receiver incorrectly resetting the metadata for which key an encryptionroot is encrypted by.