Agreed, unless we can figure out how to use each line bidirectionally, which I would prefer. Especially since it would let us generate stereo audio as well.
Don't forget we also have the USB lines, which might eventually be more interesting than the 3 pin serial port - even if each pin of the 2.5 mm jack can only be used for its original purpose (i.e. not like on the TI calcs), a network where TX is through the USB and RX is through the 3 pin port can still be possible, assuming we figure out how to control at least one of the USB lines. If we learn to control two lines on the USB, then we can forget about the 3 pin port (or use it for other purposes while keeping network connection on the USB).
IIRC there was someone hacking around the USB, what were the results?
And by the way, I know I can probably find this out reading some documentation, but what is the maximum baudrate achievable for the 3 pin serial port (I mean technically, not the one used in file transfer, unless file transfer uses the maximum)?.