Most modern notebooks (or even desktops) don't have serial or parallel ports, making configuring management routers and switches and industrial machines like PLC's or HMI panels extremely difficult or impossible. Sometimes USB converters work, but they are problematic, especially if you need to use older programs that are written to talk directly to the hardware.
This is where the ThinkPad Serial / Parallel Port Bay Adapter comes in. It's an Ultrabay Slim device that works on the T60, T61, and R60. The adapter does not work on the R61, any of the Z series, or anything older than the 6x series. Some of the older ThinkPads have a parallel port, and you will have to use the docking station to get a serial port.
When the adapter is inserted into the Ultrabay, the serial and parallel ports will show up in the device manager and in the BIOS. They are true hardware ports.
The adapter and my T60.
The adapter uses the middle connector in the Ultrabay.
Inserted into my T60.
Connected to a router board.
Showing up in Device Manager.
True hardware ports.
Update 12/23/2008: I finally got to see a ThinkPad T400 in person. And unfortunately, the T400 does not appear to have the middle connector in the Ultrabay necessary for the serial / parallel adapter.
Looks like my next ThinkPad will be the X200 for portability.