IMHO, the best solutions that I have seen are with a serial receiver
mounted to the top of a backpack, shoulder or even a hat.
These units are around the size of a computer mouse, some smaller, some
larger, the etrek being a good standalone size with a serial interface
option... some of the smaller standalone units do not have a serial
Building a custom serial/GPS power cable can make a major difference in
portability and the user can either keep the serial cord attached to the
PPC or plug it in when they power the PPC up... your program would be
active and have them tap a screen button to record the location and then
either enter the necessary data with the stylus or voice recorder.
In addition, you can save a significant amount of power by powering down
the PPC's screen but allowing your software to continue to track between
The "plug in" pcmcia/CF units will be more portable, but, as you noted,
they will demand more of the PPC's power, plus it has been my experience
that a powered up GPS unit will take several minutes to get a "fix" and
that fix will not be as accurate as the fix from a unit that has been
powered up and tracking for a while.
Hope this helps...