Wonnink discovered that a Googlebot visited his website through IPv6 on 18 july 2010, as it appeared in his website logs. From the log it becomes clear only the robots.txt has been requested. Although that doesn't seem like much, the bot is indeed IPv6 only, as the FQDN resolves back to the IPv6 address.

Good news Google! It's about time. Click here for the article at Fix6, including the logs.