Until there are common sites that are only accessible via IPv6 -- thus unavailable to "unevolved" ISP customers, ISP won't be investing anything in IPv6 deployment. That's not to say ISPs aren't experimenting with it -- some are, simply that they are not putting any heavy engineering resources behind it.
I beg to differ. I know several ISPs that have been quietly putting quite a bit of engineering resource behind IPv6. The public announcement of residential IPv6 trials by Comcast was not the beginning of a serious commitment to IPv6 by Comcast, but, rather more towards the middle. Comcast has had substantial engineering resources on IPv6 for several years now. Will IPv6-only content be common soon? Probably not for at least another 5 years. Will IPv6-only eye-balls with severely degraded IPv4 customer experiences be common sooner? You bet. That one is unavoidable as there simply won't be IPv4 address space to use for some significant fraction of those customers. Owen