I've definitely seen it on linux.
I'm using 9vx as my primary development platform, and even though it's
fantastic to have a Plan 9 environment so easily setup and integrated
to the host OS, it has its limits. For example it will crash if your
badly written program tries to read on a hanged up connection, or it
will freeze if you run a buggy program in acid with truss.

Still, it's so convenient compared to dual booting or qemu that I prefer
sticking with it.

Cheers,
Mathieu