The laptop I use can also run Windows XP when it is really necessary (every time this happens most of the time is spent waiting on windows updates). So I enabled IPv6 on Windows XP. IPv6 works nicely. I disabled the 'privacy extensions' directly because I want traceable addresses in use, even with IPv6.
The one application that goes horribly wrong now is the webbrowser Opera. When the laptop is in a non-IPv6 enabled network (like at work) and I visit an IPv6-enabled website like weather.idefix.net with it, it fails horribly: it just shows a 'network error' page after a long timeout. Disabling automatic 6to4 makes the 'network error' page just appear faster. I reported this as an bug with Opera. Other browsers (Internet explorer, Firefox) don't show this error (but I need to test them with IPv6 to make sure they don't avoid it completely).