Turning on the "block all incoming IPv6 connections" option will also break: 1) active mode FTP from the local network to public IPv6 servers; 2) IPv6/IPsec with ISAKMP/IKE; 3) Quicktime streaming over IPv6; 4) BitTorrent sharing with IPv6; 5) certain VoIP applications; 7) anything else that communicates over more than one socket and relies on inbound flows to work.

It breaks all these things in exchange for protection against all those evil IPv6 worms we keep hearing about in the news all the time. Why, I've heard that an unprotected Mac OS X computer hooked up to the IPv6 Internet without a firewall protecting it will be completely owned by mob hackers from Port Watson in less than fifteen seconds. TURN ON YOUR FIREWALLS!!!