Google just posted an announcement on Google App Engine Blog: App Engine and IPv6, Round 2. This announces that ghs.google.com now has an IPv6 address, although, as with many other Google hostnames, the IPv6 address is only visible if your organisation or ISP has been "whitelisted" for IPv6/AAAA records in Google's DNS.
In addition, Google have added an alternate name, ghs46.google.com, that announces both traditional IP (IPv4) and IPv6 addresses even for non-whitelisted users. This allows users of Google Apps to "opt-in" to IPv6. One example where you can do this is if you have your blog hosted on Blogger, but use your own domain name - like this blog. I have already changed blog.simon.leinen.ch to point to ghs46, so if you have IPv6 connectivity, you might already have loaded this blog post over IPv6.