I've had issues this year w/ Ubuntu 14.04 machines where the kernel modules would not build, resulting in zpools that could not be imported. I guess that's more of a packaging issue than a code issue.

I periodically have unexpected behavior where my filesystem doesnt mount right and I have to re-mount, or the nfs exports have to be re-exported, etc. I've assumed this was due to incomplete configuration on my part but it's clearly not as brainless to set up as native fs.