Well, the point is that I set up IPv6 on my LAN to try it out, so turning of advertisments kind of defeats the purpose
I'll have a look if it is possible to set radvd to a lower log level.
BTW, the ip6tables rules from your homepage worked as a charm (just had to edit the interface since I use 6to4). Now the port scanner reported stealth on all ports on my MythTV backend.