I'm pleased to report that (having fixed the IPv6 on my home WiFi), my HTC Desire S running Android 2.3 picks up an auto-configured IPv6 address on its WiFi interface. This is then used successfully by the built-in browser, K9 Mail and Irssi Connectbot.

I was hoping to include a screenshot showing the IPv6 address the phone had obtained, but apparently you can only screenshot a non-rooted Android by using the developer tools ... sounds like a job for another day.