When I made some changes to the network stuff around here recently, I left the IPv6 stuff turned on, thinking one day I would look into how it works.
Turns out I have been using it for some time:
tcp6 0 0 fe80:1::230:1bff.22 fe80:1::20a:95ff.56141 ESTABLISHED
I had no idea, though it did make me jump to see a connection to port 22 over IPv6. Those addresses are a little opaque at first glance.