I don't know the percentages, but several of the big home broadband ISPs are supporting native IPv6 via dual-stacking all the way to the customer premises. If you have a DOCSIS 3.0 modem, I believe that Cox and Comcast will both give you a IPv6 address via DHCPv6, at least in most areas. (I know that both of them do in Northern VA, it may not be universal particularly for Comcast.)
Many users aren't even aware of this, though, because the number of consumer-grade routers that support IPv6 is very small. I think that the Apple Airport may be one of the few, along with a few higher-end Linksys/Cisco ones (although lots of $100+ Linksys units don't, and they seem to be in absolutely no hurry to implement it via firmware updates -- I'm sure they see it as an opportunity to sell new hardware in a few years).
Consumers don't know to look for "IPv6" as a feature when they're buying a router, and so as a result Linksys et al don't bother to include it, and so even though a user might have a fully IPv6-capable uplink, there's no way to use it short of plugging their computer directly into their modem.