After a while of not having it working, I've managed to get IPv6 connectivity back to my house from the office. Huzzah! Now I can work around the broken Juniper VPN that we normally use.
Having got this working again (it's a combination of OpenVPN and the MacOS X port of the tun driver), I've rediscovered that AFP file sharing works over IPv6, like it used to in Tiger. Not only that, but Screen Sharing works over IPv6 too! The only hiccup there is that so far as I can tell, Screen Sharing can't figure out how to connect to IPv6 only DNS names. I've tried flushing the DS cache (with dscacheutil -flushcache), but that doesn't seem to help (nor was it necessary to get AFP by DNS name to work). Connecting to literal IPv6 addresses (wrapped with square brackets), however, does work.
So Big Ups to Apple for their commitment to IPv6! Now they just have to fix that one thing.