When I load my world and open it for LAN and my brother tries to join with his MAC he gets this error: "Internal exception: java.io.IOException: Received string length longer than maximum allowwed (18 > 16)".
He got it with 1.4 and after updating to 1.4.2.
When he loads a game and opens it for LAN and I try to join with my PC I just get a "connect" (Timeout) error without more details.

Does joining from PC to MAC and vice versa not work?

We tried it with a "normal" WLAN via our FritzBox 7270 and with a private Hotspot over WLAN from our iPad 3 with iOS 6.