Thanks, crutschow! Just had one quick follow up question on saturation voltage. Please correct me if I've written anything wrong.
Limitations In the Low State:
Output sink current - the maximum current the output of the device can sink
Saturation voltage - the lowest the output can go in the low state???? ie why people say it does not always go to perfectly down to zero volts?
Limitations In the High State:
Output leakage current - the maximum current let out of the pin.