I was assuming that smittyj was referring to a PND type GPS device. You could probably hack into that puck and grab the signal before it goes into their PL2303 chip (same USB-->Serial chip we use in the USB-1). Actually, I would expect PNDs have the NMEA signal somewhere in their guts, too, but figuring out where to hack in to tap the data would be a trick (and a warranty defeating one, at that).
Yep, I was being "lay" with RS232 rather than precise for the purpose of brevity.
We've looked at the On-The-Go option, but it really limits you to a single compatible device (or maybe a small handful) with no simple ability for forward compatibility...if your compatible device is discontinued, the port quickly loses its utility.