reply to Mike Wolf
Re: [IPv6] Residential IPv6 rDNS In general it means that doing a reverse lookup of a residential IPv6 address doesn't return anything. This affects services that require valid reverse DNS for anti-spam/IP reputation purposes and affects systems that attempt reverse lookups in order to display a more friendly name rather than an IP address.
The AUP comments above are likely due to the primary reasons you would want rDNS, and that is to run servers, especially mail servers, which typically wont work at all without valid rDNS. In this case you probably want a business account, which as far as I know will in fact make rDNS entries for you.
In my case, for residential use, I am mostly interested in setting up dns to individually ID my home machines (now that IPv6 actually gives you more than one address). Because IPv6 addresses are so much longer and harder to remember this is almost exclusively done with DNS now.
So if I log into a website or SSH or something that says "your last login was from xxx" usually they will do an rDNS lookup and show you that instead of the IP. Game servers often use rDNS to list participants. At work it is nice to be able to catch traffic from my home machines in our stats/monitoring at a glance.
It is trivial to set up forward DNS (so you can type ssh foo.mynetwork.net) but reverse DNS has to be either performed or delegated by the ISP.