I've got a block of ipv6 addresses from A&A which I intend to have a go with. Will check out v5 when I get home. I'd be very interested to see how easy it is to get it working. Although I'm not 100% sure how useful it's going to be in the short term.

As a side note, it appears upping the MTU has made my VPN over 3G issues disappear as well.