[thwarted]

A lot of websites that resolved to AAAA didn't have a working server on the other side.

It seems that IPv6 is a mere afterthought for most content providers

IPv6 via Tunnelbroker.net actually worked better than ISP-provided-native-v6

Sounds more like a problem with your ISP's IPv6 support than the content providers. It seems unlikely that someone would go to the trouble to add an IPv6 address to DNS if they didn't have a working server up. It's much more likely that crappy ISPs don't have their IPv6 infrastructure set up correctly.