Google has some interesting stats on IPv6 usage: http://www.google.com/intl/en/ipv6/statistics.html

Currently ~2.53% of traffic going through Google is over IPv6. Adoption Rates:

    Belgium: 4.1%
    Peru: 4.26%
    USA: 4.88%
    France: 4.91%
    Germany: 5.24%
    Romania: 7.63%
    Switzerland: 9.47%