Hmm another thing to think about is the Arduino's serial port support Parity bits, although the Serial library doesn't seem to let you set that up. Maybe one of the USART registers can be tweaked after "Serial.begin(xxx)" is run.
It also supports a fancy packet mode where one master can send messages to many slaves and slave Arduinos only report bytes if the address header matches their slave address. Doubt the Serial library supports that but who knows.