Here's a fun one:
1310397101.830 416 X TCP_MISS/200 700 GET http://www.freebsd.org/layout/images/front_get_back.png adrian DIRECT/[2001:4f8:fff6::22] image/png
1310397101.835 413 X TCP_MISS/200 851 GET http://www.freebsd.org/layout/images/front_get_tr.png adrian DIRECT/18.104.22.168 image/png
Since the ipcache code already balances outbound connections between multiple hosts, any IPv6 hosts get similarly load balanced.. between IPv4 hosts as well.
I may end up adding in logic to connect to "only v4" and "only v6" in forward.c...